International Nuclear Information System (INIS)
Lange, H.
1991-01-01
Experimental investigations of crack growth under creep and creep-fatigue conditions are presented. The experiments were performed with the austenitic steel AISI 316L, that will be used in fast breeder reactors. A comparison of crack propagation behaviour at temperatures of T = 550deg C and T = 700deg C in common through-thickness cracked specimens and in plates containing surface cracks is carried out by application of several fracture mechanics parameters. The quantitative description of crack initiation times and crack velocities is persued particularly. The propagation rate of one-dimensional cracks under cyclic loading conditions at T = 550deg C is also treated with fracture mechanical methods. The influence of the hold periods on crack speed is discussed. (orig.) [de
Fatigue and Creep Crack Propagation behaviour of Alloy 617 in the Annealed and Aged Conditions
Energy Technology Data Exchange (ETDEWEB)
Julian K. Benz; Richard N. Wright
2013-10-01
The crack propagation behaviour of Alloy 617 was studied under various conditions. Elevated temperature fatigue and creep-fatigue crack growth experiments were conducted at 650 and 800 degrees C under constant stress intensity (triangle K) conditions and triangular or trapezoidal waveforms at various frequencies on as-received, aged, and carburized material. Environmental conditions included both laboratory air and characteristic VHTR impure helium. As-received Alloy 617 displayed an increase in the crack growth rate (da/dN) as the frequency was decreased in air which indicated a time-dependent contribution component in fatigue crack propagation. Material aged at 650°C did not display any influence on the fatigue crack growth rates nor the increasing trend of crack growth rate with decreasing frequency even though significant microstructural evolution, including y’ (Ni3Al) after short times, occurred during aging. In contrast, carburized Alloy 617 showed an increase in crack growth rates at all frequencies tested compared to the material in the standard annealed condition. Crack growth studies under quasi-constant K (i.e. creep) conditions were also completed at 650 degrees C and a stress intensity of K = 40 MPa9 (square root)m. The results indicate that crack growth is primarily intergranular and increased creep crack growth rates exist in the impure helium environment when compared to the results in laboratory air. Furthermore, the propagation rates (da/dt) continually increased for the duration of the creep crack growth either due to material aging or evolution of a crack tip creep zone. Finally, fatigue crack propagation tests at 800 degrees C on annealed Alloy 617 indicated that crack propagation rates were higher in air than impure helium at the largest frequencies and lowest stress intensities. The rates in helium, however, eventually surpass the rates in air as the frequency is reduced and the stress intensity is decreased which was not observed at 650
Fatigue crack propagation under elastic plastic medium at elevated temperature
International Nuclear Information System (INIS)
Asada, Y.; Yuuki, R.; Sakon, T.; Sunamoto, D.; Tokimasa, K.; Makino, Y.; Kitagawa, M; Shingai, K.
1980-01-01
The purposes of the present study are to establish the testing method to obtain compatible data on the low cycle fatigue crack propagation at elevated temperature, and to investigate the parameter controlling the crack propagation rate. In the present study, the preliminary experiments have been carried out on low cycle fatigue crack propagation behaviour in type 304 stainless steel in air at 550 0 C, using two types of specimen with a through thickness notch. Both strain controlled and stress controlled fatigue tests have been done under a fully reversed strain or stress cycling. The data obtained are correlated with some fracture mechanics parameters and are discussed with the appropriate parameter for evaluating the low cycle fatigue crack propagation behaviour at elevated temperature. (author)
Estimation of stepwise crack propagation in ceramic laminates with strong interfaces
Directory of Open Access Journals (Sweden)
K. Štegnerová
2015-10-01
Full Text Available During the last years many researchers put so much effort to design layered structures combining different materials in order to improve low fracture toughness and mechanical reliability of the ceramics. It has been proven, that an effective way is to create layered ceramics with strongly bonded interfaces. After the cooling process from the sintering temperature, due to the different coefficients of thermal expansion of individual constituents of the composite, significant internal residual stresses are developed within the layers. These stresses can change the crack behaviour. This results to the higher value of so-called apparent fracture toughness, i.e. higher resistance of the ceramic laminate to the crack propagation. The contribution deals with a description of the specific crack behaviour in the layered alumina-zirconia ceramic laminate. The main aim is to clarify crack behaviour in the compressive layer and provide computational tools for estimation of crack behaviour in the field of strong residual stresses. The crack propagation was investigated on the basis of linear elastic fracture mechanics. Fracture parameters were computed numerically and by author’s routines. Finite element models were developed in order to obtain a stress distribution in the laminate containing a crack and to simulate crack propagation. The sharp change of the crack propagation direction was estimated using Sih’s criterion based on the strain energy density factor. Estimated crack behaviour is qualitatively in a good agreement with experimental observations. Presented approach contributes to the better understanding of the toughening mechanism of ceramic laminates and can be advantageously used for design of new layered ceramic composites and for better prediction of their failure.
Notch fatigue crack propagation - A consistent concept for calculating flawed service life
International Nuclear Information System (INIS)
Dankert, M.
1999-01-01
The research report presents a consistent concept of elastic-plastic fatigue fracture mechanics, to be used for numerical description of crack initiation and propagation behaviour within and out of notched areas of circular notched specimens for Woehler tests, two-phase fatigue tests and tests under service conditions. It is shown that a fracture-mechanics approach yields results capable of describing the load history over the whole service life of a structural member. A J-integral-related crack propagation model is derived that takes into account the crack opening and closure behaviour. The model is based on specially developed formulas, algorithms and approximation formulas required for description of crack opening and closure behaviour as well as calculation of the stress intensity factor K and the J-integral of cracks at notches. The values relating to crack opening were compared with experimental data, and those describing the stress intensity factor K and the J-integrals with 2D and 3D elastic-plastic FE calculations. Good and very good agreement of results was achieved. (orig./CB) [de
3D ductile crack propagation within a polycrystalline microstructure using XFEM
Beese, Steffen; Loehnert, Stefan; Wriggers, Peter
2018-02-01
In this contribution we present a gradient enhanced damage based method to simulate discrete crack propagation in 3D polycrystalline microstructures. Discrete cracks are represented using the eXtended finite element method. The crack propagation criterion and the crack propagation direction for each point along the crack front line is based on the gradient enhanced damage variable. This approach requires the solution of a coupled problem for the balance of momentum and the additional global equation for the gradient enhanced damage field. To capture the discontinuity of the displacements as well as the gradient enhanced damage along the discrete crack, both fields are enriched using the XFEM in combination with level sets. Knowing the crack front velocity, level set methods are used to compute the updated crack geometry after each crack propagation step. The applied material model is a crystal plasticity model often used for polycrystalline microstructures of metals in combination with the gradient enhanced damage model. Due to the inelastic material behaviour after each discrete crack propagation step a projection of the internal variables from the old to the new crack configuration is required. Since for arbitrary crack geometries ill-conditioning of the equation system may occur due to (near) linear dependencies between standard and enriched degrees of freedom, an XFEM stabilisation technique based on a singular value decomposition of the element stiffness matrix is proposed. The performance of the presented methodology to capture crack propagation in polycrystalline microstructures is demonstrated with a number of numerical examples.
International Nuclear Information System (INIS)
Provot, B.; Herter, P.
2000-01-01
In order to improve the mechanical behaviour of materials used as neutron absorbers in nuclear reactors, we have developed CERCER or CERMET composites with boron and hafnium. Thus a new composite B 4 C/HfB 2 has been especially studied. We have identified three kinds of degradation under irradiation (thermal gradient, swelling due to fission products and accidental corrosion) that induce imposed deformations cracking phenomena. Mechanical behaviour and crack propagation resistance have been studied by ball-on-three-balls and double torsion tests. A special device was developed to enable crack propagation and associated stress intensity factor measurements. Effects of structure and of a second phase are underline. First results show that these materials present crack initiation and propagation resistance much higher than pure boron carbide or hafnium diboride. We observe R-Curves effects, crack bridging or branching, crack arrests, and toughness increases that we can relate respectively to the composite structures. (author)
Fatigue crack propagation behavior under creep conditions
International Nuclear Information System (INIS)
Ohji, Kiyotsugu; Kubo, Shiro
1991-01-01
The crack propagation behavior of the SUS 304 stainless steel under creep-fatigue conditions was reviewed. Cracks propagated either in purely time-dependent mode or in purely cycle-dependent mode, depending on loading conditions. The time-dependent crack propagation rate was correlated with modified J-integral J * and the cycle-dependent crack propagation rate was correlated with J-integral range ΔJ f . Threshold was observed in the cycle-dependent crack propagation, and below this threshold the time-dependent crack propagation appeared. The crack propagation rates were uniquely characterized by taking the effective values of J * and ΔJ f , when crack closure was observed. Change in crack propagation mode occurred reversibly and was predicted by the competitive damage model. The threshold disappeared and the cycle-dependent crack propagation continued in a subthreshold region under variable amplitude conditions, where the threshold was interposed between the maximum and minimum ΔJ f . (orig.)
Modelling of fatigue crack propagation assisted by gaseous hydrogen in metallic materials
International Nuclear Information System (INIS)
Moriconi, C.
2012-01-01
Experimental studies in a hydrogenous environment indicate that hydrogen created by surface reactions, then drained into the plastic zone, leads to a modification of deformation and damage mechanisms at the fatigue crack tip in metals, resulting in a significant decrease of crack propagation resistance. This study aims at building a model of these complex phenomena in the framework of damage mechanics, and to confront it with the results of fatigue crack propagation tests in high pressure hydrogen on a 15-5PH martensitic stainless steel. To do so, a cohesive zone model was implemented in the finite element code ABAQUS. A specific traction-separation law was developed, which is suitable for cyclic loadings, and whose parameters depend on local hydrogen concentration. Furthermore, hydrogen diffusion in the bulk material takes into account the influence of hydrostatic stress and trapping. The mechanical behaviour of the bulk material is elastic-plastic. It is shown that the model can qualitatively predict crack propagation in hydrogen under monotonous loadings; then, the model with the developed traction-separation law is tested under fatigue loading. In particular, the simulated crack propagation curves without hydrogen are compared to the experimental crack propagation curves for the 15-5PH steel in air. Finally, simulated fatigue crack propagation rates in hydrogen are compared to experimental measurements. The model's ability to assess the respective contributions of the different damage mechanisms (HELP, HEDE) in the degradation of the crack resistance of the 15-5PH steel is discussed. (author)
Fatigue crack layer propagation in silicon-iron
Birol, Y.; Welsch, G.; Chudnovsky, A.
1986-01-01
Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.
Estimation of stepwise crack propagation in ceramic laminates with strong interfaces
Czech Academy of Sciences Publication Activity Database
Náhlík, Luboš; Štegnerová, Kateřina; Hutař, Pavel
2015-01-01
Roč. 9, č. 34 (2015), s. 116-124 ISSN 1971-8993. [International Conference on Crack Paths /5./. Ferrara, 16.09.2015-18.09.2015] R&D Projects: GA ČR(CZ) GA15-09347S Institutional support: RVO:68081723 Keywords : Ceramic laminates * Crack behaviour * Residual stresses * Strain energy density factor * Crack propagation direction Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.34.12
Steady-state propagation of interface corner crack
DEFF Research Database (Denmark)
Veluri, Badrinath; Jensen, Henrik Myhre
2013-01-01
Steady-state propagation of interface cracks close to three-dimensional corners has been analyzed. Attention was focused on modeling the shape of the interface crack front and calculating the critical stress for steady-state propagation of the crack. The crack propagation was investigated...... on the finite element method with iterative adjustment of the crack front to estimate the critical delamination stresses as a function of the fracture criterion and corner angles. The implication of the results on the delamination is discussed in terms of crack front profiles and the critical stresses...... for propagation and the angle of intersection of the crack front with the free edge....
High temperature initiation and propagation of cracks in 12%Cr-steel turbine disks
Directory of Open Access Journals (Sweden)
S. Foletti
2013-10-01
Full Text Available This work aims to study the crack propagation in 12%Cr steel for turbine disks. Creep Crack Growth (CCG tests on CT specimens have been performed to define the proper fracture mechanics which describes the initiation of the crack propagation and the crack growth behaviour for the material at high temperature. Results have been used to study the occurrence of crack initiation on a turbine disk at the extreme working temperature and stress level experienced during service, and validate the use of C* integral in correlating creep growth rate on the disk component, in case C* is numerically calculated through FEM analysis or calculated by the use of reference stress concept.
Crack Propagation by Finite Element Method
Directory of Open Access Journals (Sweden)
Luiz Carlos H. Ricardo
2018-01-01
Full Text Available Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FDandE SAE Keyhole Specimen Test Load Histories by finite element analysis. To understand the crack propagation processes under variable amplitude loading, retardation effects are observed
Crack Propagation by Finite Element Method
H. Ricardo, Luiz Carlos
2017-01-01
Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FD&E SAE Keyh...
Directory of Open Access Journals (Sweden)
L.Y. Yang
2014-07-01
Full Text Available During the drill-and-blast progress in rock tunnel excavation of great deep mine, rock fracture is evaluated by both blasting load and pre-exiting earth stress (pre-compression. Many pre-existing flaws in the rock mass, like micro-crack, also seriously affect the rock fracture pattern. Under blasting load with pre-compression, micro-cracks initiate, propagate and grow to be wing cracks. With an autonomous design of static-dynamic loading system, dynamic and static loads were applied on some PMMA plate specimen with pre-existing crack, and the behaviour of the wing crack was tested by caustics corroding with a high-speed photography. Four programs with different static loading modes that generate different pre-compression fields were executed, and the length, velocity of the blasting wing crack and dynamic stress intensity factor (SIF at the wing crack tip were analyzed and discussed. It is found that the behaviour of blasting-induced wing crack is affected obviously by blasting and pre-compression. And pre-compression, which is vertical to the direction of the wing crack propagation, hinders the crack propagation. Furthermore, the boundary constraint condition plays an important role on the behaviour of blasting induced crack during the experiment.
Curvilinear crack layer propagation
Chudnovsky, Alexander; Chaoui, Kamel; Moet, Abdelsamie
1987-01-01
An account is given of an experiment designed to allow observation of the effect of damage orientation on the direction of crack growth in the case of crack layer propagation, using polystyrene as the model material. The direction of crack advance under a given loading condition is noted to be determined by a competition between the tendency of the crack to maintain its current direction and the tendency to follow the orientation of the crazes at its tip. The orientation of the crazes is, on the other hand, determined by the stress field due to the interaction of the crack, the crazes, and the hole. The changes in craze rotation relative to the crack define the active zone rotation.
International Nuclear Information System (INIS)
Bian, H.B.; Jia, Y.; Shao, J.F.
2012-01-01
Document available in extended abstract form only. This subject is devoted to numerical analysis of crack initiation and propagation in concrete structures due to hydro-mechanical coupling processes. When the structures subjected to the variation in hydraulic conditions, fractures occur as a consequence of coalescence of diffuse damage. Consequently, the mechanical behaviour of concrete is described by an isotropic damage model. Once the damage reaches a critical value, a macroscopic crack is initiated. In the framework of extended Finite Element Method (XFEM), the propagation of localized crack is studied in this paper. Each crack is then considered as a discontinuity surface of displacement. According to the determination of crack propagation orientations, a tensile stress-based criterion is used. Furthermore, spatial variations of mechanical properties of concrete are also taken into account using the Weibull distribution function. Finally, the proposed model is applied to numerical analysis of a concrete liner in the context of feasibility studies for geological storage of radioactive wastes. The numerical results show that the proposed approach is capable to reproduce correctly the initiation and propagation crack process until the complete failure of concrete structures during hydro-mechanical loading. The concrete is most widely used construction material in many engineering applications. It is generally submitted to various environmental loading: such as the mechanical loading, the variation of relative humidity and the exposure to chemical risk, etc. In order to evaluate the safety and durability of concrete structures, it is necessary to get a good knowledge on the influence of loading path on the concrete behaviour. The objective of this paper is to study numerically the crack propagation in concrete structure under hydro-mechanical loading,.i.e. the mechanical behaviour of concrete subjected to drying process. The drying process leads to desiccation
Hughes, Cris E; White, Crystal A
2009-03-01
This study presents a new method for understanding postmortem heat-induced crack propagation patterns in teeth. The results demonstrate that patterns of postmortem heat-induced crack propagation differ from perimortem and antemortem trauma-induced crack propagation patterns. Dental material of the postmortem tooth undergoes dehydration leading to a shrinking and more brittle dentin material and a weaker dentin-enamel junction. Dentin intertubule tensile stresses are amplified by the presence of the pulp cavity, and initiates crack propagation from the internal dentin, through the dentin-enamel junction and lastly the enamel. In contrast, in vivo perimortem and antemortem trauma-induced crack propagation initiates cracking from the external surface of the enamel toward the dentin-enamel junction where the majority of the energy of the crack is dissipated, eliminating the crack's progress into the dentin. These unique patterns of crack propagation can be used to differentiate postmortem taphonomy-induced damage from antemortem and perimortem trauma in teeth.
International Nuclear Information System (INIS)
RodrIguez-MartInez, R; Urriolagoitia-Calderon, G; Urriolagoitia-Sosa, G; Hernandez-Gomez, L H; Merchan-Cruz, E A; RodrIguez-Canizo, R G; Sandoval-Pineda, J M
2009-01-01
In this paper, the case of Single Edge Notch (SEN) specimens subject to opening/compressive loading was analyzed; The loads are applied in several ratios to evaluate the influence of the specimen geometry, and the Stress Intensity Factor (SIF) K 1 values on the directional stability of crack propagation. The main purpose of this work is to evaluate the behaviour of the fracture propagation, when modifying the geometry of the SEN specimen and different relationships of load tension/compression are applied. Additionally, the precision of the numerical and experimental analysis is evaluated to determine its reliability when solving this type of problems. The specimens are subjected to biaxial opening/compression loading; both results (numerical and experimental) are compared in order to evaluate the condition of directional stability on crack propagation. Finally, an apparent transition point related to the length of specimens was identified, in which the behaviour of values of SIF changes for different loading ratios.
Energy Technology Data Exchange (ETDEWEB)
RodrIguez-MartInez, R; Urriolagoitia-Calderon, G; Urriolagoitia-Sosa, G; Hernandez-Gomez, L H [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME), Edificio 5. 2do Piso, Unidad Profesional Adolfo Lopez Mateos ' Zacatenco' Col. Lindavista, C.P. 07738, Mexico, D.F. (Mexico); Merchan-Cruz, E A; RodrIguez-Canizo, R G; Sandoval-Pineda, J M, E-mail: rrodriguezm@ipn.m, E-mail: urrio332@hotmail.co, E-mail: guiurri@hotmail.co, E-mail: luishector56@hotmail.co, E-mail: eamerchan@gmail.co, E-mail: ricname@hotmail.co, E-mail: jsandovalp@ipn.m [Instituto Politecnico Nacional Seccion de Estudios de Posgrado e Investigacion (SEPI), Escuela Superior de IngenierIa Mecanica y Electrica (ESIME). Unidad profesional, AZCAPOTZALCO, Av. de las Granjas No. 682, Col. Sta. Catarina Azcapotzalco, C.P. 02550, Mexico D.F. (Mexico)
2009-08-01
In this paper, the case of Single Edge Notch (SEN) specimens subject to opening/compressive loading was analyzed; The loads are applied in several ratios to evaluate the influence of the specimen geometry, and the Stress Intensity Factor (SIF) K{sub 1} values on the directional stability of crack propagation. The main purpose of this work is to evaluate the behaviour of the fracture propagation, when modifying the geometry of the SEN specimen and different relationships of load tension/compression are applied. Additionally, the precision of the numerical and experimental analysis is evaluated to determine its reliability when solving this type of problems. The specimens are subjected to biaxial opening/compression loading; both results (numerical and experimental) are compared in order to evaluate the condition of directional stability on crack propagation. Finally, an apparent transition point related to the length of specimens was identified, in which the behaviour of values of SIF changes for different loading ratios.
FATIGUE CRACK PROPAGATION THROUGH AUSTEMPERED DUCTILE IRON MICROSTRUCTURE
Directory of Open Access Journals (Sweden)
Lukáš Bubenko
2010-10-01
Full Text Available Austempered ductile iron (ADI has a wide range of application, particularly for castings used in automotive and earth moving machinery industries. These components are usually subjected to variable dynamic loading that may promote initiation and propagation of fatigue cracks up to final fracture. Thus, it is important to determine the fatigue crack propagation behavior of ADI. Since fatigue crack growth rate (da/dN vs. stress intensity factor K data describe fatigue crack propagation resistance and fatigue durability of structural materials, da/dN vs. Ka curves of ADI 1050 are reported here. The threshold amplitude of stress intensity factor Kath is also determined. Finally, the influence of stress intensity factor amplitude to the character of fatigue crack propagation through the ADI microstructure is described.
Adaptive numerical modeling of dynamic crack propagation
International Nuclear Information System (INIS)
Adouani, H.; Tie, B.; Berdin, C.; Aubry, D.
2006-01-01
We propose an adaptive numerical strategy that aims at developing reliable and efficient numerical tools to model dynamic crack propagation and crack arrest. We use the cohesive zone theory as behavior of interface-type elements to model crack. Since the crack path is generally unknown beforehand, adaptive meshing is proposed to model the dynamic crack propagation. The dynamic study requires the development of specific solvers for time integration. As both geometry and finite element mesh of the studied structure evolve in time during transient analysis, the stability behavior of dynamic solver becomes a major concern. For this purpose, we use the space-time discontinuous Galerkin finite element method, well-known to provide a natural framework to manage meshes that evolve in time. As an important result, we prove that the space-time discontinuous Galerkin solver is unconditionally stable, when the dynamic crack propagation is modeled by the cohesive zone theory, which is highly non-linear. (authors)
Experimental studies of the crack behaviour during elastoplastic deformations of materials
International Nuclear Information System (INIS)
Hollstein, R.
1982-01-01
In C-, SEN- and WOL X-samples of the materials StE 460 (Ni-V), 22NiCr37, and 30CrNiMo8 a transition from linear elasticity to elastoplastic behaviour is observed with increasing temperature. Before crack propagation can be observed, a stretching zone at the crack tip is formed, which depends on the material and the stress conditions. (DG) [de
A model for high-cycle fatigue crack propagation
Energy Technology Data Exchange (ETDEWEB)
Balbi, Marcela Angela [Rosario National Univ. (Argentina); National Council of Scientific Research and Technology (CONICET) (Argentina)
2017-02-01
This paper deals with the prediction of high-cycle fatigue behavior for four different materials (7075-T6 alloy, Ti-6Al-4 V alloy, JIS S10C steel and 0.4 wt.-% C steel) using Chapetti's approach to estimate the fatigue crack propagation curve. In the first part of the paper, a single integral equation for studying the entire propagation process is determined using the recent results of Santus and Taylor, which consider a double regime of propagation (short and long cracks) characterized by the model of El Haddad. The second part of the paper includes a comparison of the crack propagation behavior model proposed by Navarro and de los Rios with the one mentioned in the first half of this work. The results allow us to conclude that the approach presented in this paper is a good and valid estimation of high-cycle fatigue crack propagation using a single equation to describe the entire fatigue crack regime.
Crack propagation of brittle rock under high geostress
Liu, Ning; Chu, Weijiang; Chen, Pingzhi
2018-03-01
Based on fracture mechanics and numerical methods, the characteristics and failure criterions of wall rock cracks including initiation, propagation, and coalescence are analyzed systematically under different conditions. In order to consider the interaction among cracks, adopt the sliding model of multi-cracks to simulate the splitting failure of rock in axial compress. The reinforcement of bolts and shotcrete supporting to rock mass can control the cracks propagation well. Adopt both theory analysis and simulation method to study the mechanism of controlling the propagation. The best fixed angle of bolts is calculated. Then use ansys to simulate the crack arrest function of bolt to crack. Analyze the influence of different factors on stress intensity factor. The method offer more scientific and rational criterion to evaluate the splitting failure of underground engineering under high geostress.
Crack propagation along polymer/non-polymer interfaces
Vellinga, Willem-Pier; Fedorov, Alexander; De Hosson, Jeff T.
2007-01-01
Mechanisms of the propagation of crack fronts along interfaces between a glassy polymer and metal or glass are discussed. Specifically, the systems studied are Poly-Ethylene Terephthalate (PETG) spin-coated on A1, PETG-glass and PETG hot-pressed on Cr-sputtered glass. Cracks studied propagate in an
Crack propagation studies and bond coat properties in thermal
Indian Academy of Sciences (India)
High threshold load at the interface between the ceramic layer and the bond coat was required to propagate the crack further into the bond coat. Once the threshold load was surpassed the crack propagated into the brittle bond coat without an appreciable increase in the load. At temperatures of 800°C the crack propagated ...
Analysis of 3D crack propagation by microfocus computed tomography
International Nuclear Information System (INIS)
Ao Bo; Chen Fuxing; Deng Cuizhen; Zeng Yabin
2014-01-01
The three-point bending test of notched specimens of 2A50 forging aluminum was performed by high frequency fatigue tester, and the surface cracks of different stages were analyzed and contrasted by SEM. The crack was reconstructed by microfocus computed tomography, and its size, position and distribution were visually displayed through 3D visualization. The crack propagation behaviors were researched through gray value and position of crack front of 2D CT images in two adjacent stages, and the results show that crack propagation is irregular. The projection image of crack was obtained if crack of two stages projected onto the reference plane respectively, a significant increase of new crack propagation was observed compared with the previous projection of crack, and the distribution curve of crack front of two stages was displayed. The 3D increment distribution of the crack front propagation was obtained through the 3D crack analysis of two stages. (authors)
Crack Growth Behaviour of P92 Steel Under Creep-fatigue Interaction Conditions
Directory of Open Access Journals (Sweden)
JING Hong-yang
2017-05-01
Full Text Available Creep-fatigue interaction tests of P92 steel at 630℃ under stress-controlled were carried out, and the crack propagation behaviour of P92 steel was studied. The fracture mechanism of crack growth under creep-fatigue interaction and the transition points in a-N curves were analyzed based on the fracture morphology. The results show that the fracture of P92 steel under creep-fatigue interaction is creep ductile fracture and the (Ctavg parameter is employed to demonstrate the crack growth behaviour; in addition, the fracture morphology shows that the crack growth for P92 steel under creep-fatigue interaction is mainly caused by the nucleation and growth of the creep voids and micro-cracks. Furthermore, the transition point of a-lg(Ni/Nf curve corresponds to the turning point of initial crack growth changed into steady crack growth while the transition point of (da/dN-N curve exhibits the turning point of steady creep crack growth changed into the accelerated crack growth.
Atomistics of crack propagation
International Nuclear Information System (INIS)
Sieradzki, K.; Dienes, G.J.; Paskin, A.; Massoumzadeh, B.
1988-01-01
The molecular dynamic technique is used to investigate static and dynamic aspects of crack extension. The material chosen for this study was the 2D triangular solid with atoms interacting via the Johnson potential. The 2D Johnson solid was chosen for this study since a sharp crack in this material remains stable against dislocation emission up to the critical Griffith load. This behavior allows for a meaningful comparison between the simulation results and continuum energy theorems for crack extension by appropriately defining an effective modulus which accounts for sample size effects and the non-linear elastic behavior of the Johnson solid. Simulation results are presented for the stress fields of moving cracks and these dynamic results are discussed in terms of the dynamic crack propagation theories, of Mott, Eshelby, and Freund
Crack propagation on spherical pressure vessels
International Nuclear Information System (INIS)
Lebey, J.; Roche, R.
1975-01-01
The risk presented by a crack on a pressure vessel built with a ductile steel cannot be well evaluated by simple application of the rules of Linear Elastic Fracture Mechanics, which only apply to brittle materials. Tests were carried out on spherical vessels of three different scales built with the same steel. Cracks of different length were machined through the vessel wall. From the results obtained, crack initiation stress (beginning of stable propagation) and instable propagation stress may be plotted against the lengths of these cracks. For small and medium size, subject to ductile fracture, the resulting curves are identical, and may be used for ductile fracture prediction. Brittle rupture was observed on larger vessels and crack propagation occurred at lower stress level. Preceedings curves are not usable for fracture analysis. Ultimate pressure can be computed with a good accuracy by using equivalent energy toughness, Ksub(1cd), characteristic of the metal plates. Satisfactory measurements have been obtained on thin samples. The risks of brittle fracture may then judged by comparing Ksub(1cd) with the calculated K 1 value, in which corrections for vessel shape are taken into account. It is thus possible to establish the bursting pressure of cracked spherical vessels, with the help of two rules, one for brittle fracture, the other for ductile instability. A practical method is proposed on the basis of the work reported here
Fatigue crack propagation in aluminum-lithium alloys
Rao, K. T. V.; Ritchie, R. O.; Piascik, R. S.; Gangloff, R. P.
1989-01-01
The principal mechanisms which govern the fatigue crack propagation resistance of aluminum-lithium alloys are investigated, with emphasis on their behavior in controlled gaseous and aqueous environments. Extensive data describe the growth kinetics of fatigue cracks in ingot metallurgy Al-Li alloys 2090, 2091, 8090, and 8091 and in powder metallurgy alloys exposed to moist air. Results are compared with data for traditional aluminum alloys 2024, 2124, 2618, 7075, and 7150. Crack growth is found to be dominated by shielding from tortuous crack paths and resultant asperity wedging. Beneficial shielding is minimized for small cracks, for high stress ratios, and for certain loading spectra. While water vapor and aqueous chloride environments enhance crack propagation, Al-Li-Cu alloys behave similarly to 2000-series aluminum alloys. Cracking in water vapor is controlled by hydrogen embrittlement, with surface films having little influence on cyclic plasticity.
Propagation of stress corrosion cracks in alpha-brasses
Energy Technology Data Exchange (ETDEWEB)
Beggs, Dennis Vinton [Univ. of Illinois, Urbana-Champaign, IL (United States)
1981-01-01
Transgranular and intergranular stress corrosion cracks were investigated in alpha-brasses in a tarnishing ammoniacal solution. Surface observation indicated that the transgranular cracks propagated discontinuously by the sudden appearance of a fine crack extending several microns ahead of the previous crack tip, often associated with the detection of a discrete acoustic emission (AE). By periodically increasing the deflection, crack front markings were produced on the resulting fracture surfaces, showing that the discontinuous propagation of the crack trace was representative of the subsurface cracking. The intergranular crack trace appeared to propagate continuously at a relatively blunt crack tip and was not associated with discrete AE. Under load pulsing tests with a time between pulses, Δt greater than or equal to 3 s, the transgranular fracture surfaces always exhibited crack front markings which corresponded with the applied pulses. The spacing between crack front markings, Δx, decreased linearly with Δt. With Δt less than or equal to 1.5 s, the crack front markings were in a one-to-one correspondence with applied pulses only at relatively long crack lengths. In this case, Δx = Δx* which approached a limiting value of 1 μm. No crack front markings were observed on intergranular fracture surfaces produced during these tests. It is concluded that transgranular cracking occurs by discontinuous mechanical fracture of an embrittled region around the crack tip, while intergranular cracking results from a different mechanism with cracking occurring via the film-rupture mechanism.
Fast fracture: an adiabatic restriction on thermally activated crack propagation
Energy Technology Data Exchange (ETDEWEB)
Burns, S.J.
1978-01-01
Slow, isothermal, crack propagation is widely suspected to be rate controlled by thermally activated plastic deformation in the crack tip region. Adiabatic conditions are generally established in the fracture modified material at the tip of a crack during fast fracture. The temperature of this material is not the temperature of the specimen and is generally not measured during fast fracture. Thus, a complete thermodynamic description of adiabatic crack propagation data can not be made. When the slow, isothermal, crack propagation mechanisms are assumed to be operative during adiabatic crack propagation then certain predictions can be made. For example: the changes in the driving force due to temperature and rate are always in the opposite sense; there is no minimum in the driving force versus crack velocity without a change in mechanism; the temperature rise in the crack tip fracture modified material is determined mainly by the activation enthalpy for crack propagation; the interpretation of fast fracture structural steel data from simple plastic models is suspect since these materials have dissimilar isothermal temperature dependencies.
Crack propagation at stresses below the fatigue limit.
Holden, F. C.; Hyler, W. S.; Marschall, C. W.
1967-01-01
Crack propagation for stainless steel and Ti alloy at stresses below fatigue limit, noting of alternating stress cycles crack propagation for stainless steel and Ti alloy at stresses below fatigue limit, noting role of alternating stress cycles
Fatigue crack propagation in self-assembling nanocomposites
Energy Technology Data Exchange (ETDEWEB)
Klingler, Andreas; Wetzel, Bernd [Institute for Composite Materials (IVW GmbH) Technical University of Kaiserslautern, 67633 Kaiserslautern (Germany)
2016-05-18
Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.
Fatigue crack propagation in self-assembling nanocomposites
Klingler, Andreas; Wetzel, Bernd
2016-05-01
Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.
Fatigue crack propagation in self-assembling nanocomposites
International Nuclear Information System (INIS)
Klingler, Andreas; Wetzel, Bernd
2016-01-01
Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.
Molecular dynamics simulation of propagating cracks
Mullins, M.
1982-01-01
Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.
TGO growth and crack propagation in a thermal barrier coating
Energy Technology Data Exchange (ETDEWEB)
Chen, W.R.; Archer, R.; Huang, X. [National Research Council of Canada, Ottawa, ON (Canada); Marple, B.R. [National Research Council of Canada, Boucherville, PQ (Canada)
2008-07-01
In thermal barrier coating (TBC) systems, a continuous alumina layer developed at the ceramic topcoat/bond coat interface helps to protect the metallic bond coat from further oxidation and improve the durability of the TBC system under service conditions. However, other oxides such as spinel and nickel oxide, formed in the oxidizing environment, are believed to be detrimental to TBC durability during service at high temperatures. It was shown that in an air-plasma-sprayed (APS) TBC system, post-spraying heat treatments in low-pressure oxygen environments could suppress the formation of the detrimental oxides by promoting the formation of an alumina layer at the ceramic topcoat/bond coat interface, leading to an improved TBC durability. This work presents the influence of post-spraying heat treatments in low-pressure oxygen environments on the oxidation behaviour and durability of a thermally sprayed TBC system with high-velocity oxy-fuel (HVOF)-produced Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat. Oxidation behaviour of the TBCs is evaluated by examining their microstructural evolution, growth kinetics of the thermally grown oxide (TGO) layers, as well as crack propagation during low frequency thermal cycling at 1050 C. The relationship between the TGO growth and crack propagation will also be discussed. (orig.)
Crack retardation by load reduction during fatigue crack propagation
International Nuclear Information System (INIS)
Kim, Hyun Soo; Nam, Ki Woo; Ahn, Seok Hwan; Do, Jae Yoon
2003-01-01
Fracture life and crack retardation behavior were examined experimentally using CT specimens of aluminum alloy 5083. Crack retardation life and fracture life were a wide difference between 0.8 and 0.6 in proportion to ratio of load reduction. The wheeler model retardation parameter was used successfully to predict crack growth behavior. By using a crack propagation rule, prediction of fracture life can be evaluated quantitatively. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the retardation life and fracture life by the change of load reduction
Interface fatigue crack propagation in sandwich X-joints – Part I: Experiments
DEFF Research Database (Denmark)
Moslemian, Ramin; Berggreen, Christian
2013-01-01
Correlation technique was used to locate the crack tip and monitor the crack growth. For the specimens with H45 core, unstable crack growth took place initially. Following the unstable propagation, the crack propagated in the core underneath the resin-rich cell layer approaching the interface. However......, the crack did not kink into the interface. For the specimens with H100 core, the crack propagated initially in the core and then returned into the interface and continued to propagate in the interface. For the specimens with H250 core, the crack initially propagated in the core and then kinked...
Study of fatigue crack propagation in magnesium alloys
International Nuclear Information System (INIS)
Yarema, S.Ya.; Zinyuk, O.D.; Ostash, O.P.; Kudryashov, V.G.; Elkin, F.M.
1981-01-01
Fatigue crack propagation in standard (MA2-1, MA8) and super light (MA21, MA18) alloys has been investigated in the whole range of load amplitude changes-from threshold to critical; the materials have been compared by cyclic crack resistance, fractographic analysis has been made. It is shown that MA2-1 alloy crack resistance is slightly lower than the resistance of the other three alloys. MA8 and MA21 alloys having similar mechanical properties almost do not differ in cyclic crack resistance as well. MA18 alloy has the highest resistance to fatigue crack propagation in the whole range of Ksub(max) changes. The presented results on cyclic crack resistance of MA21 and MA18 alloys agree with the data on statistic fracture toughness. The fractures have been also investigated using a scanning electron microscope. Fracture microrelieves of MA8 and MA21 alloys are very similar. At low crack propagation rates (v - 7 m/cycle) it develops through grains, in MA2-1 alloy fracture intergrain fracture areas can be observed. In MA8 and MA21 alloy fractures groove covered areas can be seen alonside with areas of slipping plane laminatron; their specific weight increases with #betta# decrease. Lower crack propagation rates and higher values of threshold stress intensity factors for MA8 and MA21 alloys than for MA2-1 alloy are caused by the absence of intergrain fracture
Suppression of Fatigue Crack Propagation of Duralumin by Cavitation Peening
Directory of Open Access Journals (Sweden)
Hitoshi Soyama
2015-08-01
Full Text Available It was demonstrated in the present paper that cavitation peening which is one of the mechanical surface modification technique can suppress fatigue crack propagation in duralumin. The impacts produced when cavitation bubble collapses can be utilised for the mechanical surface modification technique in the same way as laser peening and shot peening, which is called “cavitation peening”. Cavitation peening employing a cavitating jet in water was used to treat the specimen made of duralumin Japanese Industrial Standards JIS A2017-T3. After introducing a notch, fatigue test was conducted by a load-controlled plate bending fatigue tester, which has been originally developed. The fatigue crack propagation behavior was evaluated and the relationship between the fatigue crack propagation rate versus stress intensity factor range was obtained. From the results, the fatigue crack propagation rate was drastically reduced by cavitation peening and the fatigue life of duralumin plate was extended 4.2 times by cavitation peening. In addition, the fatigue crack propagation can be suppressed by 88% in the stable crack propagation stage by cavitation peening.
Modelling probabilistic fatigue crack propagation rates for a mild structural steel
Directory of Open Access Journals (Sweden)
J.A.F.O. Correia
2015-01-01
Full Text Available A class of fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and local strain-life damage models have been proposed in literature. The fatigue crack growth is regarded as a process of continuous crack initializations over successive elementary material blocks, which may be governed by smooth strain-life damage data. Some approaches account for the residual stresses developing at the crack tip in the actual crack driving force assessment, allowing mean stresses and loading sequential effects to be modelled. An extension of the fatigue crack propagation model originally proposed by Noroozi et al. (2005 to derive probabilistic fatigue crack propagation data is proposed, in particular concerning the derivation of probabilistic da/dN-ΔK-R fields. The elastic-plastic stresses at the vicinity of the crack tip, computed using simplified formulae, are compared with the stresses computed using an elasticplastic finite element analyses for specimens considered in the experimental program proposed to derive the fatigue crack propagation data. Using probabilistic strain-life data available for the S355 structural mild steel, probabilistic crack propagation fields are generated, for several stress ratios, and compared with experimental fatigue crack propagation data. A satisfactory agreement between the predicted probabilistic fields and experimental data is observed.
Sub-critical cohesive crack propagation with hydro-mechanical coupling and friction
Directory of Open Access Journals (Sweden)
S. Valente
2016-01-01
Full Text Available Looking at the long-time behaviour of a dam, it is necessary to assume that the water can penetrate a possible crack washing away some components of the concrete. This type of corrosion reduces the tensile strength and fracture energy of the concrete compared to the same parameters measured during a short-time laboratory test. This phenomenon causes the so called sub-critical crack propagation. That is the reason why the International Commission of Large Dams recommends to neglect the tensile strength of the joint between the dam and the foundation, which is the weakest point of a gravity dam. In these conditions a shear displacement discontinuity starts growing in a point, called Fictitious Crack Tip (shortened FCT, which is still subjected to a compression stress. In order to manage this problem, in this paper the cohesive crack model is re-formulated with the focus on the shear stress component. In this context, the classical Newton-Raphson method fails to converge to an equilibrium state. Therefore the approach used is based on two stages: (a a global one in which the FCT is moved ahead of one increment; (b a local one in which the non-linear conditions occurring in the Fracture Process Zone are taken into account. This two-stage approach, which is known in the literature as a Large Time Increment method, is able to model three different mechanical regimes occurring during the crack propagation between a dam and the foundation rock.
Directory of Open Access Journals (Sweden)
Jommi Cristina
2016-01-01
Full Text Available Desiccation cracks are usually thought to start from the surface of an evaporating soil layer, and the available simplified models for crack initiation and propagation are based on this hypothesis. On the contrary, experimental results on a Dutch river clay showed that cracks in an evaporating soil layer may start and propagate below the surface, confirming earlier findings by other researchers. A simple one-dimensional model was set up to analyse the consequences of different hypotheses about the material behaviour on the crack onset in a homogenous soil layer undergoing surface drying. The results of the model show that dependence of the material behaviour on the rate of water content change is a necessary requirement for cracks to initiate below the surface. The conclusion suggests that, to properly understand cracking in an evaporating soil layer, an intrinsic time scale for the mechanical response must be accounted for, among all the other factors which were previously highlighted by other researchers. The key factor to predict crack onset below the surface is the dependence of the drying branch of the water retention curve of the compressible soil on the rate of drying, which would be justified by a rate dependent fabric evolution.
Multispecimen fatigue crack propagation testing
International Nuclear Information System (INIS)
Ermi, A.M.; Bauer, R.E.; Chin, B.A.; Straalsund, J.L.
1981-01-01
Chains of miniature center-cracked-tension specimens were tested on a conventional testing machine and on a prototypic in-reactor fatigue machine as part of the fusion reactor materials alloy development program. Annealed and 20 percent cold-worked 316 stainless steel specimens were cycled under various conditions of temperature, frequency, stress ratio and chain length. Crack growth rates determined from multispecimen visual measurements and from an electrical potential technique were consistent with those obtained by conventional test methods. Results demonstrate that multispecimen chain testing is a valid method of obtaining fatigue crack propagation information for alloy development. 8 refs
Possibility of crack propagation in first wall by cyclic electromagnetic
International Nuclear Information System (INIS)
Teramoto, T.; Saito, M.
1998-01-01
A strong electromagnetic force due to plasma disruption damages the structural integrity of fusion reactor components. If a crack is generated on disruption, this crack may propagate to a critical length by the iteration of disruption. In this study, electro-magneto-mechanical analysis is conducted to evaluate the crack behavior under various field conditions. The crack propagation life is estimated by the experimental fatigue data. (author)
Propagation of cracks and damage in non aging linear viscoelastic media
International Nuclear Information System (INIS)
Nguyen, S.T.
2010-01-01
Most of France's energy is nuclear. The reactor building comprises a internal and external containment. The internal containment is prestressed to limit the flow of leakage in the internal-external space. The prestress decreases during time by the creep of concrete. It may propagate the cracks by the accidental internal pressure. So we define two research problems: propagation of macro-cracks in viscoelastic structure; effective behavior of micro-cracked viscoelastic material. Firstly, we develop a Burger viscoelastic model of concrete with two approaches: numerical and analytical. Then we solve the problem of single cracks in developing thermodynamically the concept of energy release rate. In the third part we develop a viscoelastic model to study the effective behavior of micro-cracked materials in the case without propagation. The problem of propagation of microcracks is then studied by a numerical approach based on the 'representative pattern morphology'. These studies are finally applied to solve the problems of crack propagation and damage of containment under accidental internal pressure. (authors)
Dynamic propagation and cleavage crack arrest in bainitic steel
International Nuclear Information System (INIS)
Hajjaj, M.
2006-06-01
In complement of the studies of harmfulness of defects, generally realized in term of initiation, the concept of crack arrest could be used as complementary analyses to the studies of safety. The stop occurs when the stress intensity factor becomes lower than crack arrest toughness (KIa) calculated in elasto-statics (KI ≤ KIa). The aim of this thesis is to understand and predict the stop of a crack propagating at high speed in a 18MND5 steel used in the pressure water reactor (PWR). The test chosen to study crack arrest is the disc thermal shock test. The observations under the scanning electron microscope of the fracture surface showed that the crack arrest always occurs in cleavage mode and that the critical microstructural entity with respect to the propagation and crack arrest corresponds to at least the size of the prior austenitic grain. The numerical analyses in elasto-statics confirm the conservatism of the codified curve of the RCC-M with respect to the values of KIa. The dynamic numerical analyses show that the deceleration of the crack measured at the end of the propagation is related to the global dynamic of the structure (vibrations). The transferability to components of crack arrest toughness obtained from tests analysed in static is thus not assured. The disc thermal shock tests were also modelled by considering a criterion of propagation and arrest of the type 'RKR' characterized by a critical stress sc which depends on the temperature. The results obtained account well for the crack jump measured in experiments as well as the shape of the crack arrest front. (author)
Influence of a gaseous atmosphere on fatigue crack propagation
International Nuclear Information System (INIS)
Henaff, G.
2002-01-01
The paper presents a review of the current knowledge on the influence of gaseous atmospheres, and primarily ambient air, on fatigue crack propagation in metallic alloys. Experimental evidence of the effect of exposure to ambient air or any moist environment on fatigue crack propagation in steels is first proposed. The different interacting processes are analyzed so as to clearly uncouple the influence of the various factors on crack growth resistance. Two distinct mechanisms are identified: the adsorption of vapour molecules and hydrogen assisted fracture at crack tip. (author)
Effect of copper on crack propagation in beryllium single crystals
International Nuclear Information System (INIS)
Aldinger, F.; Wilhelm, M.
The effect of copper additives on the fracture energy and the development of cracks parallel to the basal plane was studied in zone-refined single crystalline beryllium. At 77 0 K the cleavage planes are very smooth, so the crack propagation energy, which is independent of copper content (less than 2 at. percent Cu) in the range of measurement accuracy, is only a little higher than the surface energy of the basal plane. At room temperature, due to intense plastic processes taking place in front of the crack tip, the fracture energy is an order of magnitude higher than at low temperatures. The effect of copper on the plastic processes can be divided into two regions. In region I (less than 1.2 at. percent Cu), in which the crack propagation energy increases sharply with increasing copper content, crack propagation is controlled by prism slips. The decrease in crack propagation energy in region II (greater than 1.2 at. percent Cu) can be attributed to a reduction of beryllium twinning energy with increasing copper content. (auth)
Crack propagation in dynamic thermoelasticity
International Nuclear Information System (INIS)
Bui, H.D.
1980-01-01
We study the singular thermoelastic fields near the crack tip, in the linear strain assumption. The equations are coupled and non linear. The asymptotic expansions of the displacement and the temperature are given for the first and the second order. It is shown that the temperature is singular when the crack propagates. However, this field does not change the dominant singularity of the mechanical field which is the same as that obtained in the theory of isothermal elasticity [fr
Study of regularities in propagation of thermal fatigue cracks
International Nuclear Information System (INIS)
Tachkova, N.G.; Sobolev, N.D.; Egorov, V.I.; Rostovtsev, Yu.V.; Ivanov, Yu.S.; Sirotin, V.L.
1978-01-01
Regularities in the propagation of thermal fatigue cracks in the Cr-Ni steels of the austenite class depending upon deformation conditions in the crack zone, have been considered. Thin-walled tube samples of the Kh16N40, Kh18N20 and Kh16N15 steels have been tested in the 10O reversible 400 deg C and 100 reversible 500 deg C regimes. The samples have possessed a slot-shaped stress concentrator. Stress intensity pseudocoefficient has been calculated for the correlation of experimental data. The formula for determining crack propagation rate has been obtained. The experiments permit to conclude that propagation rate of thermal fatigue cracks in the above steels depends upon the scope of plastic deformation during a cycle and stress intensity pseudocoefficient, and is determined by plastic deformation resistance during thermal cyclic loading
Heat affected zone and fatigue crack propagation behavior of high performance steel
International Nuclear Information System (INIS)
Choi, Sung Won; Kang, Dong Hwan; Kim, Tae Won; Lee, Jong Kwan
2009-01-01
The effect of heat affected zone in high performance steel on fatigue crack propagation behavior, which is related to the subsequent microstructure, was investigated. A modified Paris-Erdogan equation was presented for the analysis of fatigue crack propagation behavior corresponding to the heat affected zone conditions. Fatigue crack propagation tests under 0.3 stress ratio and 0.1 load frequency were conducted for both finegrained and coarse-grained heat affected zones, respectively. As shown in the results, much higher crack growth rate occurred in a relatively larger mean grain size material under the same stress intensity range of fatigue crack propagation process for the material.
Analysis of crack propagation in concrete structures with structural information entropy
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The propagation of cracks in concrete structures causes energy dissipation and release, and also causes energy redistribution in the structures. Entropy can characterize the energy redistribution. To investigate the relation between the propagation of cracks and the entropy in concrete structures, cracked concrete structures are treated as dissipative structures. Structural information entropy is defined for concrete structures. A compact tension test is conducted. Meanwhile, numerical simulations are also carried out. Both the test and numerical simulation results show that the structural information entropy in the structures can characterize the propagation of cracks in concrete structures.
International Nuclear Information System (INIS)
Shirakihara, Kaori; Tanaka, Keisuke; Akiniwa, Yoshiaki; Suzuki, Yasuyoshi; Mukai, Hirokatsu
2006-01-01
Fatigue crack propagation tests of PZT specimens were performed under cyclic four-point bending with and without superposition of electric fields. The specimens were poled in the longitudinal direction (PL specimens) perpendicular to the crack plane. The crack propagation rate for the case of open circuit was faster than that for the case of short circuit. The application of a negative or positive electric field parallel to the poling direction accelerated the crack propagation rate, and the amount of acceleration was larger for the case of the negative field. The change of the crack propagation rate with crack extension can be divided into three regions. In the region I, the crack propagation rate decreases with increasing crack length, and then turn to increase in the region III. In the region II, the propagation rate is nearly constant. The mechanisms of fatigue crack propagation were correlated to domain switching near the crack tip. The grain boundary fracture was predominant in the low-rate region, while transgranular fracture became abundant on the unstable fracture surface. (author)
Numerical investigation on the prefabricated crack propagation of FV520B stainless steel
Directory of Open Access Journals (Sweden)
Juyi Pan
Full Text Available FV520B is a common stainless steel for manufacturing centrifugal compressor impeller and shaft. The internal metal flaw destroys the continuity of the material matrix, resulting in the crack propagation fracture of the component, which seriously reduces the service life of the equipment. In this paper, Abaqus software was used to simulate the prefabricated crack propagation of FV520B specimen with unilateral gap. The results of static crack propagation simulation results show that the maximum value of stress–strain located at the tip of the crack and symmetrical distributed like a butterfly along the prefabricated crack direction, the maximum stress is 1990 MPa and the maximum strain is 9.489 × 10−3. The Mises stress and stress intensity factor KI increases with the increase of the expansion step, the critical value of crack initiation is reached at the 6th extension step. The dynamic crack propagation simulation shows that the crack propagation path is perpendicular to the load loading direction. Similarly, the maximum Mises stress located at the crack tip and is symmetrically distributed along the crack propagation direction. The critical stress range of the crack propagation is 23.3–43.4 MPa. The maximum value of stress–strain curve located at the 8th extension step, that is, the crack initiation point, the maximum stress is 55.22 MPa, and the maximum strain is 2.26 × 10−4. On the crack tip, the stress changed as 32.24–40.16 MPa, the strain is at 1.292 × 10−4–1.897 × 10−4. Keywords: FV520B, Crack propagation, Mises stress, Stress–strain, Numerical investigation
Impacts of bedding directions of shale gas reservoirs on hydraulically induced crack propagation
Directory of Open Access Journals (Sweden)
Keming Sun
2016-03-01
Full Text Available Shale gas reservoirs are different from conventional ones in terms of their bedding architectures, so their hydraulic fracturing rules are somewhat different. In this paper, shale hydraulic fracturing tests were carried out by using the triaxial hydraulic fracturing test system to identify the effects of natural bedding directions on the crack propagation in the process of hydraulic fracturing. Then, the fracture initiation criterion of hydraulic fracturing was prepared using the extended finite element method. On this basis, a 3D hydraulic fracturing computation model was established for shale gas reservoirs. And finally, a series of studies were performed about the effects of bedding directions on the crack propagation created by hydraulic fracturing in shale reservoirs. It is shown that the propagation rules of hydraulically induced fractures in shale gas reservoirs are jointly controlled by the in-situ stress and the bedding plane architecture and strength, with the bedding direction as the main factor controlling the crack propagation directions. If the normal tensile stress of bedding surface reaches its tensile strength after the fracturing, cracks will propagate along the bedding direction, and otherwise vertical to the minimum in-situ stress direction. With the propagating of cracks along bedding surfaces, the included angle between the bedding normal direction and the minimum in-situ stress direction increases, the fracture initiation and propagation pressures increase and the crack areas decrease. Generally, cracks propagate in the form of non-plane ellipsoids. With the injection of fracturing fluids, crack areas and total formation filtration increase and crack propagation velocity decreases. The test results agree well with the calculated crack propagation rules, which demonstrate the validity of the above-mentioned model.
Directory of Open Access Journals (Sweden)
B. Vargas-Arista
2013-01-01
Full Text Available The fractography and mechanical behaviour of fatigue crack propagation in the heat-affected zone (HAZ of AISI 4140 steel welded using the shielded metal arc process was analysed. Different austenitic grain size was obtained by normalizing performed at 1200 °C for 5 and 10 hours after welding. Three point bending fatigue tests on pre-cracked specimens along the HAZ revealed that coarse grains promoted an increase in fatigue crack growth rate, hence causing a reduction in both fracture toughness and critical crack length, and a transgranular brittle final fracture with an area fraction of dimple zones connecting cleavage facets. A fractographic analysis proved that as the normalizing time increased the crack length decreased. The increase in the river patterns on the fatigue crack propagation in zone II was also evidenced and final brittle fracture because of transgranular quasicleavage was observed. Larger grains induced a deterioration of the fatigue resistance of the HAZ.
Ductile cast irons: microstructure influence on fatigue crack propagation resistance
Directory of Open Access Journals (Sweden)
Mauro Cavallini
2010-07-01
Full Text Available Microstructure influence on fatigue crack propagation resistance in five different ductile cast irons (DCI was investigated. Four ferrite/pearlite volume fractions were considered, performing fatigue crack propagation tests according to ASTM E647 standard (R equals to 0.1, 0.5 and 0.75, respectively. Results were compared with an austempered DCI. Damaging micromechanisms were investigated according to the following procedures: - “traditional” Scanning Electron Microscope (SEM fracture surfaces analysis; - SEM fracture surface analysis with 3D quantitative analysis; - SEM longitudinal crack profile analysis - Light Optical Microscope (LOM transversal crack profile analysis;
Biaxial fatigue crack propagation behavior of perfluorosulfonic-acid membranes
Lin, Qiang; Shi, Shouwen; Wang, Lei; Chen, Xu; Chen, Gang
2018-04-01
Perfluorosulfonic-acid membranes have long been used as the typical electrolyte for polymer-electrolyte fuel cells, which not only transport proton and water but also serve as barriers to prevent reactants mixing. However, too often the structural integrity of perfluorosulfonic-acid membranes is impaired by membrane thinning or cracks/pinholes formation induced by mechanical and chemical degradations. Despite the increasing number of studies that report crack formation, such as crack size and shape, the underlying mechanism and driving forces have not been well explored. In this paper, the fatigue crack propagation behaviors of Nafion membranes subjected to biaxial loading conditions have been investigated. In particular, the fatigue crack growth rates of flat cracks in responses to different loading conditions are compared, and the impact of transverse stress on fatigue crack growth rate is clarified. In addition, the crack paths for slant cracks under both uniaxial and biaxial loading conditions are discussed, which are similar in geometry to those found after accelerated stress testing of fuel cells. The directions of initial crack propagation are calculated theoretically and compared with experimental observations, which are in good agreement. The findings reported here lays the foundation for understanding of mechanical failure of membranes.
Subsurface crack initiation and propagation mechanisms in gigacycle fatigue
International Nuclear Information System (INIS)
Huang Zhiyong; Wagner, Daniele; Bathias, Claude; Paris, Paul C.
2010-01-01
In the very high cycle regime (N f > 10 7 cycles) cracks can nucleate on inclusions, 'supergrains' and pores, which leads to fish-eye propagation around the defect. The initiation from an inclusion or other defect is almost equal to the total crack growth lifetime, perhaps much more than 99% of this lifetime in many cases. Integration of the Paris law allows one to predict the number of cycles to crack initiation. A cyclic plastic zone around the crack exists, and recording the surface temperature of the sample during the test may allow one to follow crack propagation and determine the number of cycles to crack initiation. A thermo-mechanical model has been developed. In this study several fish-eyes from various materials have been observed by scanning electron microscopy, and the fractographic results analyzed as they related to the mechanical and thermo-mechanical models.
On the mechanism of crack propagation resistance of fully lamellar TiAl alloy
International Nuclear Information System (INIS)
Cao, R.; Yao, H.J.; Chen, J.H.; Zhang, J.
2006-01-01
The study was done using notched two-colony thick tensile specimens of a directionally solidified cast fully lamellar TiAl alloy. In-situ observations of fracture processes in scanning electron microscope (SEM) were combined with section-to-section related observations of fracture surfaces to investigate the crack growth process. Finite element method (FEM) calculations are carried out to evaluate the stresses for propagating cracks. The results reveal that: (1) the reason why enhancement of applied load is required to propagate the main crack, was attributed to that the main crack observed at the surface did not extend all the way through the specimen's thickness thus the stress field was still controlled by the notch, in which a definite stress required for extending a crack tip should be kept by increasing the applied load. (2) Crack propagation resistance is enhanced at colony boundaries, only when a change occurs from an inter-lamellar propagation to a trans-lamellar propagation (3) Ligament bridging toughening phenomena can be integrated into aforementioned mechanism. As a whole the processes of new crack nucleation with bridging ligament formation decreases the crack propagation resistance rather than increasing it. (4) In case the majority of microcracks are surface cracks, the effect of microcrack shielding is not obvious
Crack propagation behavior of TiN coatings by laser thermal shock experiments
International Nuclear Information System (INIS)
Choi, Youngkue; Jeon, Seol; Jeon, Min-seok; Shin, Hyun-Gyoo; Chun, Ho Hwan; Lee, Youn-seoung; Lee, Heesoo
2012-01-01
Highlights: ► The crack propagation behavior of TiN coating after laser thermal shock experiment was observed by using FIB and TEM. ► Intercolumnar cracks between TiN columnar grains were predominant cracking mode after laser thermal shock. ► Cracks were propagated from the coating surface to the substrate at low laser pulse energy and cracks were originated at coating-substrate interface at high laser pulse energy. ► The cracks from the interface spread out transversely through the weak region of the columnar grains by repetitive laser shock. - Abstract: The crack propagation behavior of TiN coatings, deposited onto 304 stainless steel substrates by arc ion plating technique, related to a laser thermal shock experiment has been investigated using focused ion beam (FIB) and transmission electron microscopy (TEM). The ablated regions of TiN coatings by laser ablation system have been investigated under various conditions of pulse energies and number of laser pulses. The intercolumnar cracks were predominant cracking mode following laser thermal shock tests and the cracks initiated at coating surface and propagated in a direction perpendicular to the substrate under low loads conditions. Over and above those cracks, the cracks originated from coating-substrate interface began to appear with increasing laser pulse energy. The cracks from the interface also spread out transversely through the weak region of the columnar grains by repetitive laser shock.
In-reactor fatigue crack propagation
International Nuclear Information System (INIS)
Ermi, A.M.; Mervyn, D.A.; Straalsund, J.L.
1979-08-01
An in-reactor fatigue experiment is being designed to determine the effect of dynamic irradiation on the fatigue crack propagation (FCP) behavior of candidate fusion first wall materials. This investigation has been prompted by studies which show gross differences in crack growth characteristics of creep rupture specimens testing by postirradiation versus dynamic in-reactor methods. The experiment utilizes miniature center-cracked-tension specimens developed specifically for in-reactor studies. In the test, a chain of eight specimens, precracked to various initial crack lengths, is stressed during irradiation to determine crack growth rate as a function of stress intensity. Load levels were chosen which result in small crack growth rates encompassing a regime of the crack growth curve not previously investigated during irradiation studies of FCP. The test will be conducted on 20% cold worked 316 stainless steel at a temperature of 425 0 C, in a sodium environment, and at a frequency of 1 cycle/min. Irradiation will occur in the Oak Ridge Research Reactor, resulting in a He/dpa ratio similar to that expected at the first wall in a fusion reactor. Detailed design of the experiment is presented, along with crack growth data obtained from prototypic testing of the experimental apparatus. These results are compared to data obtained under similar conditions generated by conventional test methods
Effect of short-term overloads on crack propagation under creep
International Nuclear Information System (INIS)
Sushok, V.V.; Sobolev, N.D.; Zolotukhin, S.Yu.
1986-01-01
Kinetics of crack propagation after overload has been studied using plane samples of Kh18N10T steel. Tests of samples with a notch have been carried out in the air at 293 K. Observation of the crack growth has been carried out by the microscope and the method of electric potential difference. It is established that during overload besides crack tip blunting, decrease of creep rate of the material stregthened near it, that leads to crack retardation, decrease of plasticity and formation of microcracks in front of the tip of the main-line crack occurs. It is marked that, estimating serviceability of a member, it is necessary to take into account the decrease of crack propagation rate after short term overloads
The influence of creep properties on crack propagation in thermal barrier coatings
International Nuclear Information System (INIS)
Baeker, Martin
2010-01-01
Thermal barrier coatings are used to protect turbine blades from the high temperature of the process gas inside a turbine. They consist of a metallic bond coat and of a ceramic top coat with low thermal conductivity. During service, an additional oxide layer forms between bond coat and top coat that eventually causes failure. Finite element simulations show that the roughness of the interface between top and bond coat is crucial for determining the stress state. Lifetime models have been inferred that assume that cracks form in the peak positions at small oxide thickness and propagate when the oxide layer grows and the stress field shifts. A two-dimensional finite element model of crack propagation in the TBC layer is presented. Since the cracks propagate near a material interface and since plasticity may occur in the bond coat, standard tools of fracture mechanics for predicting the crack propagation direction are difficult to apply. This problem is circumvented in a very simple way by propagating short 'test cracks' in different directions and optimising to find the crack direction with the maximum energy release rate. It is shown that the energy release rate and the crack propagation direction are sensitive to the details of the stress state and especially to the creep properties of the materials. Implications for failure models are discussed.
International Nuclear Information System (INIS)
Kamaya, Masayuki; Chiba, Goro; Nakajima, Nobuo; Totsuka, Nobuo
2001-01-01
Environmentally assisted crack initiation behavior is greatly affected by applied stress and environmental factors, such as water temperature, contained impurities and so on. On the other hand, crack initiation behavior also influences crack propagation. A typical example of this influence can be observed as the interference effects of multiple cracks, such as the coalescence of approaching crack tips or the arrest phenomena in the relaxation zone of an adjacent crack. To understand these effects of crack initiation on crack propagation behavior is very important to predict the lifetime of components, in which quite a few cracks tend to occur. This study aimed at revealing the crack initiation behavior and the influence of this behavior on propagation. At first, to evaluate the effect of applied stress on crack initiation behavior, sensitized stainless steel was subjected to a four-point bending test in a high temperature water environment at the constant potentials of ECP +50 mV and ECP +150 mV. Secondly, a crack initiation and growth simulation model was developed, in which the interference effect of multiple cracks is evaluated by the finite element method, based on the experimental results. Using this model, the relationship between crack initiation and propagation was studied. From the model, it was revealed that the increasing number of the cracks accelerates crack propagation and reduces life. (author)
Energy Technology Data Exchange (ETDEWEB)
Kamaya, Masayuki; Chiba, Goro; Nakajima, Nobuo; Totsuka, Nobuo [Institute of Nuclear Safety System Inc., Mihama, Fukui (Japan)
2001-09-01
Environmentally assisted crack initiation behavior is greatly affected by applied stress and environmental factors, such as water temperature, contained impurities and so on. Crack initiation behavior also influences crack propagation. A typical example of this influence can be observed as the interference effects of multiple cracks, such as the coalescence of approaching crack tips or the arrest phenomena in the relaxation zone of an adjacent crack. To understand these effects of crack initiation on crack propagation behavior is very important to predict the lifetime of components, in which relatively large number of cracks tend to occur. This study aimed at revealing the crack initiation behavior and the influence of this behavior on propagation. At first, to evaluate the effect of applied stress on crack initiation behavior, sensitized stainless steel was subjected to a four-point bending test in high temperature water environment at the constant potentials of +50 mV SHE and +150 mV SHE Secondly, a crack initiation and growth simulation model was developed, in which the interference effect of multiple cracks is evaluated by the finite element method, based on the experimental results. Using this model, the relationship between crack initiation and propagation was investigated, and it was revealed that the increasing number of the cracks accelerates crack propagation and reduces life. (author)
Effect of wetting-drying cycles on soil desiccation cracking behaviour
Directory of Open Access Journals (Sweden)
Tang Chao-Sheng
2016-01-01
Full Text Available Better understanding the desiccation cracking process is essential in analysing drought effects on soil hydraulic and mechanical properties through consideration of the atmosphere-ground interaction. Laboratory tests were conducted to investigate the consequence of wetting-drying cycles on the initiation and propagation characteristics of desiccation cracks on soil surface. Initially saturated slurry specimens were prepared and subjected to five subsequent wetting-drying cycles. Image processing technique was employed to quantitatively analyze the morphology characteristics of crack patterns formed during each drying path. The results show that the desiccation cracking behaviour of soil is significantly affected by the wetting-drying cycles. Before the third wetting-drying cycle is reached, the surface crack ratio and the average crack width increases while the average clod area decreases with increasing the number of wetting-drying cycles. The number of intersections and crack segments per unit area reaches the peak values after the second wetting-drying cycle. After the third wetting-drying cycle is reached, the effect of increasing wetting-drying cycles on crack patterns is insignificant. Moreover, it is observed that the applied wetting-drying cycles are accompanied by a continual reconstruction of soil structure. The initial homogenous slurry structure is completely replaced with aggregated structure after the third cycles, and a significant increase in the inter-aggregate porosity can be observed.
Low temperature fatigue crack propagation in neutron irradiated Type 316 steel and weld metal
International Nuclear Information System (INIS)
Lloyd, G.J.; Walls, J.D.; Gravenor, J.
1981-02-01
The fast cycling fatigue crack propagation characteristics of Type 316 steel and weld metal have been investigated at 380 0 C after irradiation to 1.72-1.92x10 20 n/cm 2 (E>1MeV) and 2.03x10 21 n/cm 2 (E>1MeV) at the same temperature. With mill-annealed Type 316 steel, modest decreases in the rates of crack propagation were observed for both dose levels considered, whereas for cold-worked Type 316 steel irradiation to 2.03x10 21 n/cm 2 (E>1MeV) caused increases in the rate of crack propagation. For Type 316 weld metal, increases in the rate of crack propagation were observed for both dose levels considered. The diverse influences of irradiation upon fatigue crack propagation in these materials are explained by considering a simple continuum mechanics model of crack propagation together with the results of control tensile experiments made on similarly irradiated materials. (author)
Experimental study of fatigue crack propagation in type 316 austenitic stainless steel
International Nuclear Information System (INIS)
Mostafa, M.; Vessiere, G.; Hamel, A.; Boivin, M.
1983-01-01
In this work, are grouped and compared the crack propagation rates in type 316 austenitic stainless steel in two loading cases: plane strain and plane stress. Plane strain has been obtained on axisymmetric cracked specimens, plane stress on thin notched specimens, subjected to alternative bending. The results show that the crack propagation rate is greater for plane strain, i.e. in the case of the smallest plastic zone. The Elber concept was also used for explaining the different values of the crack propagation rate. It's noteworthy to find out that the Paris' law coefficients for different loading levels and those fo Elber's law are correlated [fr
International Nuclear Information System (INIS)
Menouillard, T.
2007-09-01
Computerized simulation is nowadays an integrating part of design and validation processes of mechanical structures. Simulation tools are more and more performing allowing a very acute description of the phenomena. Moreover, these tools are not limited to linear mechanics but are developed to describe more difficult behaviours as for instance structures damage which interests the safety domain. A dynamic or static load can thus lead to a damage, a crack and then a rupture of the structure. The fast dynamics allows to simulate 'fast' phenomena such as explosions, shocks and impacts on structure. The application domain is various. It concerns for instance the study of the lifetime and the accidents scenario of the nuclear reactor vessel. It is then very interesting, for fast dynamics codes, to be able to anticipate in a robust and stable way such phenomena: the assessment of damage in the structure and the simulation of crack propagation form an essential stake. The extended finite element method has the advantage to break away from mesh generation and from fields projection during the crack propagation. Effectively, crack is described kinematically by an appropriate strategy of enrichment of supplementary freedom degrees. Difficulties connecting the spatial discretization of this method with the temporal discretization of an explicit calculation scheme has then been revealed; these difficulties are the diagonal writing of the mass matrix and the associated stability time step. Here are presented two methods of mass matrix diagonalization based on the kinetic energy conservation, and studies of critical time steps for various enriched finite elements. The interest revealed here is that the time step is not more penalizing than those of the standard finite elements problem. Comparisons with numerical simulations on another code allow to validate the theoretical works. A crack propagation test in mixed mode has been exploited in order to verify the simulation
Infrared thermography study of the fatigue crack propagation
Directory of Open Access Journals (Sweden)
O.A. Plekhov
2012-07-01
Full Text Available The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone.
Hilyati, S.; Nizam, Z. M.; Zurisman, M. A. A.; Azhar, A. T. S.
2017-06-01
During the last two decades, reinforced concrete (RC) has been extensively used in most of the world as one of the common construction material due to its advantages and durability. However, RC structures exposed to marine environments are subjected to chloride attack. Chlorides from seawater penetrate into RC structures are not only causing severe corrosion problems but also affect the durability and serviceability of such structures. This paper investigates the influence of transverse reinforcement and spacing of reinforcing bars on concrete cover cracking of two-way RC slab specimens using accelerated corrosion tests. The experimental program involved the testing of four RC slab specimens and was generally designed to observe the crack width and the time of crack to propagate. An improved model for predicting the timing of crack propagation based on the experimental data was then developed.
A Continuum-Atomistic Analysis of Transgranular Crack Propagation in Aluminum
Yamakov, V.; Saether, E.; Glaessgen, E.
2009-01-01
A concurrent multiscale modeling methodology that embeds a molecular dynamics (MD) region within a finite element (FEM) domain is used to study plastic processes at a crack tip in a single crystal of aluminum. The case of mode I loading is studied. A transition from deformation twinning to full dislocation emission from the crack tip is found when the crack plane is rotated around the [111] crystallographic axis. When the crack plane normal coincides with the [112] twinning direction, the crack propagates through a twinning mechanism. When the crack plane normal coincides with the [011] slip direction, the crack propagates through the emission of full dislocations. In intermediate orientations, a transition from full dislocation emission to twinning is found to occur with an increase in the stress intensity at the crack tip. This finding confirms the suggestion that the very high strain rates, inherently present in MD simulations, which produce higher stress intensities at the crack tip, over-predict the tendency for deformation twinning compared to experiments. The present study, therefore, aims to develop a more realistic and accurate predictive modeling of fracture processes.
Propagation of stress-corrosion cracks in unirradiated zircaloy
International Nuclear Information System (INIS)
Norring, K.; Haag, Y.; Wikstroem, C.
1982-01-01
Propagation of iodine-induced stress-corrosion cracks in Zircaloy was studied using pre-cracked and internally pressurized cladding tubes. These were recrystallized at different temperatures, to obtain grain sizes between 4 μm and 10 μm. No statistically significant difference in propagation rate due to the difference in grain size was observed. If the obtained data, with Ksub(I) values ranging from 4 to 11 MNmsup(-3/2), were log-log plotted (da/dt = CKsub(I)sup(N)), as usual, they fell within the scatter-band of data reported earlier. But from this plot it could also be seen that the Ksub(I) interval can be divided into two separate parts having different da/dt-Ksub(I) relations. The transition takes place at a Ksub(I) value of about 8 MNmsup(-3/2). The region with lower Ksub(I) values shows a substantially lower n value than the upper region (2.4 and 9.8 respectively), and earlier reported values (n = 7 to 10). This transition is in good agreement with a transition from an intergranular to a transgranular propagation mode of the stress-corrosion crack. (orig.)
Huang, Peiyan; Liu, Guangwan; Guo, Xinyan; Huang, Man
2008-11-01
The experimental research on fatigue crack propagation rate of reinforced concrete (RC) beams strengthened with carbon fiber laminate (CFL) is carried out by MTS system in this paper. The experimental results show that, the main crack propagation on strengthened beam can be summarized into three phases: 1) fast propagation phase; 2) steady propagation and rest phase; 3) unsteady propagation phase. The phase 2-i.e. steady propagation and rest stage makes up about 95% of fatigue life of the strengthened beam. The propagation rate of the main crack, da/dN, in phase 2 can be described by Paris formula, and the constant C and m can be confirmed by the fatigue crack propagation experiments of the RC beams strengthened with CFL under three-point bending loads.
International Conference on Dynamic Crack Propagation
1973-01-01
The planning meeting for a conference on Dynamic Crack Propagation was held at M.LT. in February 1971 and attended by research workers from several industrial, governmental and academic organizations. It was felt that a more specialized meeting would provide a better opportunity for both U.S. and foreign researchers to exchange their ideas and views on dynamic fracture, a subject which is seldom emphasized in national or international fracture conferences. Dynamic crack propagation has been a concern to specialists in many fields: continuum mechanics, metallurgy, geology, polymer chemistry, orthopedics, applied mathematics, as well as structural design and testing. It impinges on a wide variety of problems such as rock breaking and earthquakes, pressure vessels and line pipes, comminution and the per formance of armament and ordnance, etc. Advances have been numerous, covering theories and experiments from both the microscopic and macro scopic points of view. Hence, the need for comparing the theoretical ...
Fatigue Crack Propagation Under Variable Amplitude Loading Analyses Based on Plastic Energy Approach
Directory of Open Access Journals (Sweden)
Sofiane Maachou
2014-04-01
Full Text Available Plasticity effects at the crack tip had been recognized as “motor” of crack propagation, the growth of cracks is related to the existence of a crack tip plastic zone, whose formation and intensification is accompanied by energy dissipation. In the actual state of knowledge fatigue crack propagation is modeled using crack closure concept. The fatigue crack growth behavior under constant amplitude and variable amplitude loading of the aluminum alloy 2024 T351 are analyzed using in terms energy parameters. In the case of VAL (variable amplitude loading tests, the evolution of the hysteretic energy dissipated per block is shown similar with that observed under constant amplitude loading. A linear relationship between the crack growth rate and the hysteretic energy dissipated per block is obtained at high growth rates. For lower growth rates values, the relationship between crack growth rate and hysteretic energy dissipated per block can represented by a power law. In this paper, an analysis of fatigue crack propagation under variable amplitude loading based on energetic approach is proposed.
Crack propagation and arrest simulation of X90 gas pipe
International Nuclear Information System (INIS)
Yang, Fengping; Huo, Chunyong; Luo, Jinheng; Li, He; Li, Yang
2017-01-01
To determine whether X90 steel pipe has enough crack arrest toughness or not, a damage model was suggested as crack arrest criterion with material parameters of plastic uniform percentage elongation and damage strain energy per volume. Fracture characteristic length which characterizes fracture zone size was suggested to be the largest mesh size on expected cracking path. Plastic uniform percentage elongation, damage strain energy per volume and fracture characteristic length of X90 were obtained by five kinds of tensile tests. Based on this criterion, a length of 24 m, Φ1219 × 16.3 mm pipe segment model with 12 MPa internal gas pressure was built and computed with fluid-structure coupling method in ABAQUS. Ideal gas state equation was used to describe lean gas behavior. Euler grid was used to mesh gas zone inside the pipe while Lagrangian shell element was used to mesh pipe. Crack propagation speed and gas decompression speed were got after computation. The result shows that, when plastic uniform percentage elongation is equal to 0.054 and damage strain energy per volume is equal to 0.64 J/mm"3, crack propagation speed is less than gas decompression speed, which means the simulated X90 gas pipe with 12 MPa internal pressure can arrest cracking itself. - Highlights: • A damage model was suggested as crack arrest criterion. • Plastic uniform elongation and damage strain energy density are material parameters. • Fracture characteristic length is suggested to be largest mesh size in cracking path. • Crack propagating simulation with coupling of pipe and gas was realized in ABAQUS. • A Chinese X90 steel pipe with 12 MPa internal pressure can arrest cracking itself.
Yuan, Shen-fang; Jin, Xin; Qiu, Lei; Huang, Hong-mei
2015-03-01
In order to improve the security of aircraft repaired structures, a method of crack propagation monitoring in repaired structures is put forward basing on characteristics of Fiber Bragg Grating (FBG) reflecting spectra in this article. With the cyclic loading effecting on repaired structure, cracks propagate, while non-uniform strain field appears nearby the tip of crack which leads to the FBG sensors' reflecting spectra deformations. The crack propagating can be monitored by extracting the characteristics of FBG sensors' reflecting spectral deformations. A finite element model (FEM) of the specimen is established. Meanwhile, the distributions of strains which are under the action of cracks of different angles and lengths are obtained. The characteristics, such as main peak wavelength shift, area of reflecting spectra, second and third peak value and so on, are extracted from the FBGs' reflecting spectral which are calculated by transfer matrix algorithm. An artificial neural network is built to act as the model between the characteristics of the reflecting spectral and the propagation of crack. As a result, the crack propagation of repaired structures is monitored accurately and the error of crack length is less than 0.5 mm, the error of crack angle is less than 5 degree. The accurately monitoring problem of crack propagation of repaired structures is solved by taking use of this method. It has important significance in aircrafts safety improvement and maintenance cost reducing.
In situ fatigue-crack-propagation experiment
International Nuclear Information System (INIS)
Ermi, A.M.; Chin, B.A.
1981-01-01
An in-reactor fatigue experiment was conducted in the Oak Ridge Research Reactor to determine the effects of dynamic irradiation on fatigue crack propagation. Eight 20% cold-worked 316 stainless steel specimens were precracked to various initial crack lengths, linked together to form a chain, and inserted into a specially designed in-reactor fatigue machine. Test conditions included a maximum temperature of 460 0 C, an environment of sodium, a frequency of 1 cycle/min, and a stress ratio of 0.10. Results indicated that (1) no effects of dynamic irradiation were observed for a fluence of 1.5 x 10 21 n/cm 2 (E > 0.1 MeV); and (2) crack growth rates in elevated temperature sodium were a factor of 3 to 4 lower than in room temperature air
Crack formation and crack propagation under multiaxial mechanical and thermal stresses. Proceedings
International Nuclear Information System (INIS)
1993-01-01
The 25th meeting of the DV Fracture Group was held on 16/17 February 1993 at Karlsruhe Technical University. The main topic, ''Crack formation and crack propagation under multiaxial mechanical and thermal stresses'', was discussed by five invited papers (by K.J. Miller, D. Loehe, H.A. Richard, W. Brocks, A. Brueckner-Foit) and 23 short papers. The other 21 papers were devoted to various domains of fracture mechanics, with emphasis on elastoplastic fracture mechanics. (orig./MM) [de
Crack propagation and the material removal mechanism of glass-ceramics by the scratch test.
Qiu, Zhongjun; Liu, Congcong; Wang, Haorong; Yang, Xue; Fang, Fengzhou; Tang, Junjie
2016-12-01
To eliminate the negative effects of surface flaws and subsurface damage of glass-ceramics on clinical effectiveness, crack propagation and the material removal mechanism of glass-ceramics were studied by single and double scratch experiments conducted using an ultra-precision machine. A self-manufactured pyramid shaped single-grit tool with a small tip radius was used as the scratch tool. The surface and subsurface crack propagations and interactions, surface morphology and material removal mechanism were investigated. The experimental results showed that the propagation of lateral cracks to the surface and the interaction between the lateral cracks and radial cracks are the two main types of material peeling, and the increase of the scratch depth increases the propagation angle of the radial cracks and the interaction between the cracks. In the case of a double scratch, the propagation of lateral cracks and radial cracks between paired scratches results in material peeling. The interaction between adjacent scratches depends on the scratch depth and separation distance. There is a critical separation distance where the normalized material removal volume reaches its peak. These findings can help reduce surface flaws and subsurface damage induced by the grinding process and improve the clinical effectiveness of glass-ceramics used as biological substitute and repair materials. Copyright © 2016 Elsevier Ltd. All rights reserved.
Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history
International Nuclear Information System (INIS)
Stout, R.B.
2001-01-01
An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)
Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history
Energy Technology Data Exchange (ETDEWEB)
Stout, R.B. [California Univ., Livermore, CA (United States). Lawrence Livermore National Lab
2001-07-01
An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)
Energy Technology Data Exchange (ETDEWEB)
Ueda, Y.; Murakawa, H. [Osaka Univ., Osaka (Japan). Welding Research Inst.; Tanigawa, M. [Hitachi Zosen Corp., Osaka (Japan)
1996-12-31
In order to investigate an effect of the plastic deformation, which was generated on ship side outer platings subjected to collision load before crack initiation, on the crack propagation behavior, crack propagation experiments using pre-strained specimens and simulation analysis by means of FEM method were carried out, to discuss about the practical simulation analysis method. As a result of the crack propagation experiments using pre-strained center notched plate specimens, a phenomenon where the crack is apt to propagate due to the pre-strains was confirmed, and measured data of crack tip opening angles were obtained. A method was proposed, in which the critical crack tip opening angle values are corrected by considering the difference between the crack shapes obtained from the FEM analysis model and actually measured, and its effectiveness was confirmed. The finite element size effect was also examined. A method using an equivalent plastic strain as the crack propagation condition was shown to determine the relationship between the element size and the critical value of equivalent plastic strain. 5 refs., 21 figs., 4 tabs.
Energy Technology Data Exchange (ETDEWEB)
Ueda, Y; Murakawa, H [Osaka Univ., Osaka (Japan). Welding Research Inst.; Tanigawa, M [Hitachi Zosen Corp., Osaka (Japan)
1997-12-31
In order to investigate an effect of the plastic deformation, which was generated on ship side outer platings subjected to collision load before crack initiation, on the crack propagation behavior, crack propagation experiments using pre-strained specimens and simulation analysis by means of FEM method were carried out, to discuss about the practical simulation analysis method. As a result of the crack propagation experiments using pre-strained center notched plate specimens, a phenomenon where the crack is apt to propagate due to the pre-strains was confirmed, and measured data of crack tip opening angles were obtained. A method was proposed, in which the critical crack tip opening angle values are corrected by considering the difference between the crack shapes obtained from the FEM analysis model and actually measured, and its effectiveness was confirmed. The finite element size effect was also examined. A method using an equivalent plastic strain as the crack propagation condition was shown to determine the relationship between the element size and the critical value of equivalent plastic strain. 5 refs., 21 figs., 4 tabs.
Fatigue crack propagation in neutron-irradiated ferritic pressure-vessel steels
International Nuclear Information System (INIS)
James, L.A.
1977-01-01
The results of a number of experiments dealing with fatigue crack propagation in irradiated reactor pressure-vessel steels are reviewed. The steels included ASTM alloys A302B, A533B, A508-2, and A543, as well as weldments in A543 steel. Fluences and irradiation conditions were generally typical of those experienced by most power reactors. In general, the effect of neutron irradiation on the fatigue crack propagation behavior of these steels was neither significantly beneficial nor significantly detrimental
Crack propagation and fracture in silicon carbide
International Nuclear Information System (INIS)
Evans, A.G.; Lange, F.F.
1975-01-01
Fracture mechanics and strength studies performed on two silicon carbides - a hot-pressed material (with alumina) and a sintered material (with boron) - have shown that both materials exhibit slow crack growth at room temperature in water, but only the hot-pressed material exhibits significant high temperature slow crack growth (1000 to 1400 0 C). A good correlation of the observed fracture behaviour with the crack growth predicted from the fracture mechanics parameters shows that effective failure predictions for this material can be achieved using macro-fracture mechanics data. (author)
Energy Technology Data Exchange (ETDEWEB)
Castano, M.L.; Garcia, M.S.; Diego, G. de; Gomez-Briceno, D. [CIEMAT, Nuclear Fission Department, Structural Materials Program, Avda. Complutense 22, 28040 Madrid (Spain)
2004-07-01
Core components of light water reactor (LWR), mainly made of austenitic stainless steels (SS), subjected to stress and exposed to relatively high fast neutron flux may suffer a cracking process termed as Irradiation Assisted Stress Corrosion Cracking (IASCC). Neutron radiation leads to critical modifications in material characteristics, which can modify their stress corrosion cracking (SCC) response. Current knowledge highlights three fundamental factors, induced by radiation, as primary contributors to IASCC of core materials: Radiation Induced Segregation (RIS) at grain boundaries, Radiation Hardening and Radiolysis. Most of the existing literature on IASCC is focussed on the influence of RIS, mainly chromium depletion, which can promote IASCC in oxidizing environments, such a Boiling Water Reactor (BWR) under normal water chemistry. However, in non-oxidizing environments, such as primary water of Pressurized Water Reactor (PWR) or BWR hydrogen water chemistry, the role played by chromium depletion at grain boundary on IASCC behaviour of highly irradiated material is irrelevant. One important issue with limited study is the effect of radiation induced hardening. The role of hardening on IASCC is became stronger considered, especially for environments where other factors, like micro-chemistry, have no significant influence. To formulate the mechanism of IASCC, a well-established method is to isolate and quantify the effect of individual parameters. The use of unirradiated material and the simulation of the irradiation effects is a procedure used with success for evaluating the influence of irradiation effects. Radiation hardening can be simulated by mechanical deformation and, although some differences exist in the types of defects produced, it is believed that the study of the SCC behaviour of unirradiated materials with different hardening levels would contribute to the understanding of IASCC mechanism. In order to evaluate the influence of hardening on the
Crack growth behaviour of aluminium wrought alloys in the Very High Cycle Fatigue regime
Directory of Open Access Journals (Sweden)
Bülbül Fatih
2018-01-01
Full Text Available Investigations have shown that in the regime of Very High Cycle Fatigue (VHCF “natural” crack initiation often takes place underneath the material surface leading to crack propagation without contact to atmospheric components. In order to elucidate the environmental damage contribution and its effect on the VHCF long crack propagation, fatigue experiments with alternating environment (vacuum and laboratory air were performed. An ultrasonic fatigue testing system (USFT equipped with a small vacuum chamber was applied that enables the in-situ examination of the long fatigue crack propagation at a resonance frequency of about 20 kHz by using a long distance microscope. By means of the Focused-Ion-Beam technique, micro-notches were prepared in the USFT specimens. The tests were carried out on the aluminium alloys EN-AW 6082 and 5083 in different conditions. It has been found that the atmosphere has a significant influence on the VHCF long crack propagation which manifests itself in the crack path as well as in the crack growth rates. Because of pronounced single sliding in vacuum, shear-stress-controlled crack propagation was detected whereas in laboratory air normal-stress-controlled crack propagation occurred. Furthermore, it has been proven that the secondary precipitation state of the aluminium alloy significantly influences the VHCF long crack propagation in vacuum.
Crack propagation in touch ductile materials. Phase II
International Nuclear Information System (INIS)
Venter, R.D.; Sinclair, A.N.; McCammond, D.
1989-06-01
The thrust of this work was to investigate published J material resistance and stress-strain data applicable to the understanding of crack propagation in tough ductile steels, particularly SA 106 Grade B pipe steel. This data has been assembled from PIFRAC, AECB report INFO-0254-1 and Ontario Hydro sources and has been uniformly formatted and presented to facilitate comparison and assessment. While the data is in many aspects incomplete it has enabled an evaluation of the influence of temperature, specimen thickness and specimen orientation to be made in the context of the experimental J-R curves so determined. Comparisons of the stress-strain data within the Ramburg-Osgood formulation are also considered. A further component of this report addresses the development of the required software to utilize what is referred to as the engineering approach to elasto-plastic analysis to investigate the load carrying capacity of selected cracked pipe geometries which are representative of applied crack propagation studies associated with piping systems in the nuclear industry. Three specific geometries and loading situations, identified as Condition A, B and C have been evaluated; the results are presented and illustrate the variation in applied load as a function of an initial and final crack extension leading to instability
Effect of Chamber Pressurization Rate on Combustion and Propagation of Solid Propellant Cracks
Yuan, Wei-Lan; Wei, Shen; Yuan, Shu-Shen
2002-01-01
area of the propellant grain satisfies the designed value. But cracks in propellant grain can be generated during manufacture, storage, handing and so on. The cracks can provide additional surface area for combustion. The additional combustion may significantly deviate the performance of the rocket motor from the designed conditions, even lead to explosive catastrophe. Therefore a thorough study on the combustion, propagation and fracture of solid propellant cracks must be conducted. This paper takes an isolated propellant crack as the object and studies the effect of chamber pressurization rate on the combustion, propagation and fracture of the crack by experiment and theoretical calculation. deformable, the burning inside a solid propellant crack is a coupling of solid mechanics and combustion dynamics. In this paper, a theoretical model describing the combustion, propagation and fracture of the crack was formulated and solved numerically. The interaction of structural deformation and combustion process was included in the theoretical model. The conservation equations for compressible fluid flow, the equation of state for perfect gas, the heat conducting equation for the solid-phase, constitutive equation for propellant, J-integral fracture criterion and so on are used in the model. The convective burning inside the crack and the propagation and fracture of the crack were numerically studied by solving the set of nonlinear, inhomogeneous gas-phase governing equations and solid-phase equations. On the other hand, the combustion experiments for propellant specimens with a precut crack were conducted by RTR system. Predicted results are in good agreement with experimental data, which validates the reasonableness of the theoretical model. Both theoretical and experimental results indicate that the chamber pressurization rate has strong effects on the convective burning in the crack, crack fracture initiation and fracture pattern.
Directory of Open Access Journals (Sweden)
Hadi Haeri
Full Text Available The pre-existing cracks in the brittle substances seem to be the main cause of their failure under various loading conditions. In this study, a simultaneous analytical, experimental and numerical analysis of crack propagation, cracks coalescence and failure process of brittle materials has been performed. Brazilian disc tests are being carried out to evaluate the cracks propagation paths in rock-like Brazilian disc specimens containing single and double cracks (using rock-like specimens which are specially prepared from Portland Pozzolana Cement (PPC, fine sands and water in a rock mechanics laboratory. The failure load of the pre-cracked disc specimens are measured showing the decreasing effects of the cracks and their orientation on the final failure load. The same specimens are numerically simulated by a higher order indirect boundary element method known as displacement discontinuity method. These numerical results are compared with the existing analytical and experimental results proving the accuracy and validity of the proposed numerical method. The numerical and experimental results obtained from the tested specimens are in good agreement and demonstrate the accuracy and effectiveness of the proposed approach.
Crack closure in near-threshold fatigue crack propagation in railway axle steel EA4T
Czech Academy of Sciences Publication Activity Database
Pokorný, Pavel; Vojtek, Tomáš; Náhlík, Luboš; Hutař, Pavel
2017-01-01
Roč. 185, NOV (2017), s. 2-19 ISSN 0013-7944 R&D Projects: GA MŠk(CZ) LQ1601 Institutional support: RVO:68081723 Keywords : Fatigue crack propagation * crack closure * EA4T * Railway axle Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering , reliability analysis Impact factor: 2.151, year: 2016
A microstructural study of dynamic crack propagation in nuclear graphites
International Nuclear Information System (INIS)
Burchell, T.D.; McEnaney, B.; Tucker, M.O.; Rose, A.P.G.
1986-01-01
This paper reports a new microstructural study of dynamic crack propagation in three nuclear graphites: (i) PGA, the moderator material in UK Magnox reactors; (ii) IMl-24, the moderator material in UK Advanced gas cooled reactors (AGR); and (iii) a pitch coke graphite, which is used in the fabrication of AGR fuel sleeves. The fracture mechanisms in nuclear graphites are initiated by microcrack formation at low stresses. Typically, microcracks form in regions of well-aligned binder or at favourably-oriented pores, where stress is concentrated. With increasing applied loads, microcracks propagate taking advantage of easy cleavage paths or linking with pores. Eventually, coalescence of such cracks and inherent porosity produces a crack of critical length for fast fracture. (orig./MM)
Analysis of Crack Propagation Path on the Anisotropic Bi-Material Rock
Directory of Open Access Journals (Sweden)
Chao-Shi Chen
2010-01-01
Full Text Available This paper presents a single-domain boundary element method (SDBEM for linear elastic fracture mechanics analysis in the 2D anisotropic bimaterial. In this formulation, the displacement integral equation is collocated on the uncracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. The complete fundamental solution (Green's function for anisotropic bi-materials was also derived and implemented into the boundary integral formulation so the discretization along the interface can be avoided except for the interfacial crack part. A special crack-tip element was introduced to capture exactly the crack-tip behavior. A computer program with the FORTRAN code has been developed to effectively calculate the stress intensity factors, crack initiation angle, and propagation path of an anisotropic bi-material. This SDBEM program has been verified having a good accuracy with the previous researches. In addition, a rock of type (1/(2 disk specimen with a central crack was made to conduct the Brazilian test under diametrical loading. The result shows that the numerical analysis can predict relatively well the direction of crack initiation and the path of crack propagation.
Modeling of crack propagation in strengthened concrete disks
DEFF Research Database (Denmark)
Hansen, Christian Skodborg; Stang, Henrik
2013-01-01
Crack propagation in strengthened concrete disks is a problem that has not yet been addressed properly. To investigate it, a cracked half-infinite disk of concrete is strengthened with a linear elastic material bonded to the surface, and analyzed using two different finite element modeling...... instead of 3D calculations to predict the response of a structure and that it opens up for simpler evaluation of strengthened concrete structures using the finite element method....
International Nuclear Information System (INIS)
Tomoda, Yoshio
1981-01-01
In relation to the safe maintenance of nuclear power plants, it is necessary to prevent reactor coolant pipings from burst type failure caused by the unstable propagation of defects and cracks, such as stress corrosion cracking and fatigue cracks. In ductile materials, crack propagation is stable in tensile loading under fixed grip condition, when a specimen is controlled to deform in proportion to the increase of tensile load. However, it has been known that the instability of ductile cracks occurs after tensile load reached the maximum, especially under constant loading condition arising in the loading devices with high compliance or low tensile rigidity. In order to confirm the reliability of SUS 304 stainless pipes subjected to SCC, the crack propagation behavior was examined with the specimens having center cracks, using both testing machines with high compliance and low compliance. The instability of ductile cracks and the propagation velocity of unstable cracks were analyzed, and the calculated results were compated with the experimental results. Not only the compliance of testing machines but also the conditions of specimens affected the propagation of cracks. (Kako, I.)
International Nuclear Information System (INIS)
Le, H.N.
2009-05-01
This study aims to figure out the crack growth phenomenon by thermal fatigue induced by thermal gradient through thickness of specimen. Firstly, an experimental facility has been developed: a rectangular parallelepiped specimen is subjected to thermal cycling between 350 C and 100 C; the specimen is freed to expand and contract. Two semi-circular notches (0,1 mm depth and 4 mm length) have been machined on the surface of the specimen. A series of interrupted tests has been carried out to characterize and quantify the crack growth in depth and surface of the pre-existing crack. Next, a three-dimensional crack growth simulation has been implemented in ABAQUS. Automation using Python was used to simulate the propagation of a crack under thermal cycling, with re-meshing at crack front after each calculation step. No assumption has been taken on the crack front during the crack propagation. A comparison with test results showed very good agreement on the evolution of crack front shape and on the kinetics of propagation on the edge and the heart of pre-existing crack. An analytical approach was also developed based on the calculation of stress intensity factors (SIC). A two-dimensional approach was first introduced enabling us to better understand the influence of various thermal and geometric parameters. Finally, a three dimensional approach, with an elliptical assumption crack shape during the propagation, leading to a prediction of crack growth on the surface and in depth which is very similar to that obtained numerically, but with computational time much lower. (author)
Fatigue-crack propagation behavior of Inconel 600
International Nuclear Information System (INIS)
James, L.A.
1976-05-01
The techniques of linear-elastic fracture mechanics were employed to characterize the effects of several parameters upon the fatigue-crack propagation behavior of Inconel 600. The parameters studied included temperature, cyclic frequency, stress ratio, thermal aging, and a limited amount of testing in a liquid sodium environment
Crack propagation under conditions of low cycle fatigue
International Nuclear Information System (INIS)
Hellmann, D.
1988-01-01
A literature review is given of convenient concepts describing the mechanical behaviour of a cracked body under cyclic loading. Only the range of high growth rates is considered. However, caused by large scale yielding in this range, the application of linear elastic fracture mechanics is no longer possible. Mechanical parameters which control fatigue crack growth are a modified stress intensity factor, the J-integral, the crack tip opening displacement and a suitable strain amplitude. (orig.) With 20 figs [de
International Nuclear Information System (INIS)
Okafor, A. Chukwujekwu; Singh, Navdeep; Singh, Navrag
2007-01-01
An aircraft is subjected to severe structural and aerodynamic loads during its service life. These loads can cause damage or weakening of the structure especially for aging military and civilian aircraft, thereby affecting its load carrying capabilities. Hence composite patch repairs are increasingly used to repair damaged aircraft metallic structures to restore its structural efficiency. This paper presents the results of Acoustic Emission (AE) monitoring of crack propagation in 2024-T3 Clad aluminum panels repaired with adhesively bonded octagonal, single sided boron/epoxy composite patch under tension-tension fatigue loading. Crack propagation gages were used to monitor crack initiation. The identified AE sensor features were used to train neural networks for predicting crack length. The results show that AE events are correlated with crack propagation. AE system was able to detect crack propagation even at high noise condition of 10 Hz loading; that crack propagation signals can be differentiated from matrix cracking signals that take place due to fiber breakage in the composite patch. Three back-propagation cascade feed forward networks were trained to predict crack length based on the number of fatigue cycles, AE event number, and both the Fatigue Cycles and AE events, as inputs respectively. Network using both fatigue cycles and AE event number as inputs to predict crack length gave the best results, followed by Network with fatigue cycles as input, while network with just AE events as input had a greater error
Compressive failure with interacting cracks
International Nuclear Information System (INIS)
Yang Guoping; Liu Xila
1993-01-01
The failure processes in concrete and other brittle materials are just the results of the propagation, coalescence and interaction of many preexisting microcracks or voids. To understand the real behaviour of the brittle materials, it is necessary to bridge the gap from the relatively matured one crack behaviour to the stochastically distributed imperfections, that is, to concern the crack propagation and interaction of microscopic mechanism with macroscopic parameters of brittle materials. Brittle failure in compression has been studied theoretically by Horii and Nemat-Nasser (1986), in which a closed solution was obtained for a preexisting flaw or some special regular flaws. Zaitsev and Wittmann (1981) published a paper on crack propagation in compression, which is so-called numerical concrete, but they did not take account of the interaction among the microcracks. As for the modelling of the influence of crack interaction on fracture parameters, many studies have also been reported. Up till now, some researcher are working on crack interaction considering the ratios of SIFs with and without consideration of the interaction influences, there exist amplifying or shielding effects of crack interaction which are depending on the relative positions of these microcracks. The present paper attempts to simulate the whole failure process of brittle specimen in compression, which includes the complicated coupling effects between the interaction and propagation of randomly distributed or other typical microcrack configurations step by step. The lengths, orientations and positions of microcracks are all taken as random variables. The crack interaction among many preexisting random microcracks is evaluated with the help of a simple interaction matrix (Yang and Liu, 1991). For the subcritically stable propagation of microcracks in mixed mode fracture, fairly known maximum hoop stress criterion is adopted to compute branching lengths and directions at each tip of the crack
Fatigue crack propagation in additively manufactured porous biomaterials.
Hedayati, R; Amin Yavari, S; Zadpoor, A A
2017-07-01
Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 10 4 cycles. The test results also showed that for the same load level of 0.5F y , the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45 ° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45 ° direction with respect to the notch direction
Applicability assessment of plug weld to ITER vacuum vessel by crack propagation analysis
International Nuclear Information System (INIS)
Ohmori, Junji; Nakahira, Masataka; Takeda, Nobukazu; Shibanuma, Kiyoshi; Sago, Hiromi; Onozuka, Masanori
2006-03-01
In order to improve the fabricability of the vacuum vessel (VV) of International Thermonuclear Experimental Reactor (ITER), applicability of plug weld between VV outer shell and stiffening ribs/blanket support housings has been assessed using crack propagation analysis for the plug weld. The ITER VV is a double-wall structure of inner and outer shells with ribs and housings between the shells. For the fabrication of VV, ribs and housings are welded to outer shell after welding to inner shell. A lot of weld grooves should be adjusted for welding outer shell. The plug weld is that outer shells with slit at the weld region are set on ribs/housings then outer shells are welded to them by filling the slits with weld metal. The plug weld can allow larger tolerance of weld groove gap than ordinary butt weld. However, un-welded lengths parallel to outer sell surface remain in the plug weld region. It is necessary to evaluate the allowable un-welded length to apply the plug weld to ITER VV fabrication. For the assessment, the allowable un-welded lengths have been calculated by crack propagation analyses for load conditions, conservatively assuming the un-welded region is a crack. In the analyses, firstly allowable crack lengths are calculated from the stresses of the weld region. Then assuming initial crack length, crack propagation is calculated during operation period. Allowable initial crack lengths are determined on the condition that the propagated cracks should not exceed the allowable crack lengths. The analyses have been carried out for typical inboard straight region and inboard upper curved region with the maximum housing stress. The allowable initial cracks of ribs are estimated to be 8.8mm and 38mm for the rib and the housing, respectively, considering inspection error of 4.4mm. Plug weld between outer shell and ribs/housings could be applicable. (author)
Molecular dynamics simulation of effect of hydrogen atoms on crack propagation behavior of α-Fe
Energy Technology Data Exchange (ETDEWEB)
Song, H.Y., E-mail: gsfshy@sohu.com; Zhang, L.; Xiao, M.X.
2016-12-16
The effect of the hydrogen concentration and hydrogen distribution on the mechanical properties of α-Fe with a pre-existing unilateral crack under tensile loading is investigated by molecular dynamics simulation. The results reveal that the models present good ductility when the front region of crack tip has high local hydrogen concentration. The peak stress of α-Fe decreases with increasing hydrogen concentration. The studies also indicate that for the samples with hydrogen atoms, the crack propagation behavior is independent of the model size and boundaries. In addition, the crack propagation behavior is significantly influenced by the distribution of hydrogen atoms. - Highlights: • The distribution of hydrogen plays a critical role in the crack propagation. • The peak stress decrease with the hydrogen concentration increasing. • The crack deformation behavior is disclosed and analyzed.
FEM Modeling of Crack Propagation in a Model Multiphase Alloy
Institute of Scientific and Technical Information of China (English)
Lihe QIAN; Seishi NISHIDO; Hiroyuki TODA; Tosliro KOBAYASHI
2006-01-01
In this paper, several widely applied fracture criteria were first numerically examined and the crack-tip-region Jintegral criterion was confirmed to be more applicable to predict fracture angle in an elastic-plastic multiphase material. Then, the crack propagation in an idealized dendritic two-phase Al-7%Si alloy was modeled using an elastic-plastic finite element method. The variation of crack growth driving force with crack extension was also demonstrated. It is found that the crack path is significantly influenced by the presence of α-phase near the crack tip, and the crack growth driving force varies drastically from place to place. Lastly, the simulated fracture path in the two-phase model alloy was compared with the experimentally observed fracture path.
Effect of random microstructure on crack propagation in cortical bone tissue under dynamic loading
International Nuclear Information System (INIS)
Gao, X; Li, S; Adel-Wahab, A; Silberschmidt, V
2013-01-01
A fracture process in a cortical bone tissue depends on various factors, such as bone loss, heterogeneous microstructure, variation of its material properties and accumulation of microcracks. Therefore, it is crucial to comprehend and describe the effect of microstructure and material properties of the components of cortical bone on crack propagation in a dynamic loading regime. At the microscale level, osteonal bone demonstrates a random distribution of osteons imbedded in an interstitial matrix and surrounded by a thin layer known as cement line. Such a distribution of osteons can lead to localization of deformation processes. The global mechanical behavior of bone and the crack-propagation process are affected by such localization under external loads. Hence, the random distribution of microstructural features plays a key role in the fracture process of cortical bone. The purpose of this study is two-fold: firstly, to develop two-dimensional microstructured numerical models of cortical bone tissue in order to examine the interaction between the propagating crack and bone microstructure using an extended finite-element method under both quasi-static and dynamic loading conditions; secondly, to investigate the effect of randomly distributed microstructural constituents on the crack propagation processes and crack paths. The obtained results of numerical simulations showed the influence of random microstructure on the global response of bone tissue at macroscale and on the crack-propagation process for quasi-static and dynamic loading conditions
Fatigue crack propagation path across the dentinoenamel junction complex in human teeth.
Dong, X D; Ruse, N D
2003-07-01
The human tooth structures should be understood clearly to improve clinically used restorative materials. The dentinoenamel junction (DEJ) plays a key role in resisting crack propagation in teeth. The aim of this study was to determine the fracture toughness of the enamel-DEJ-dentin complex and to investigate the influence of the DEJ on the fatigue crack propagation path across it by characterizing fatigue-fractured enamel-DEJ-dentin complexes using optical and scanning electron microscopy. The results of this study showed that the fracture toughness of the enamel-DEJ-dentin complex was 1.50 +/- 0.28 Mpa x m(1/2). Based on the results of this investigation, it was concluded that the DEJ complex played a critical role in resisting crack propagation from enamel into dentin. The DEJ complex is, approximately, a 100 to 150 microm broad region at the interface between enamel and dentin. The toughening mechanism of the DEJ complex may be explained by the fact that crack paths were deflected as cracks propagated across it. Understanding the mechanism of crack deflection could help in improving dentin-composite as well as ceramic-cement interfacial qualities with the aim to decrease the risk of clinical failure of restorations. Both can be viewed as being composed from a layer of material of high strength and hardness bonded to a softer but tougher substratum (dentin). The bonding agent or the luting cement layer may play the critical role of the DEJ in improving the strength of these restorations in clinical situations. Copyright 2003 Wiley Periodicals, Inc.
Fatigue-crack propagation in gamma-based titanium aluminide alloys at large and small crack sizes
International Nuclear Information System (INIS)
Kruzic, J.J.; Campbell, J.P.; Ritchie, R.O.
1999-01-01
Most evaluations of the fracture and fatigue-crack propagation properties of γ+α 2 titanium aluminide alloys to date have been performed using standard large-crack samples, e.g., compact-tension specimens containing crack sizes which are on the order of tens of millimeters, i.e., large compared to microstructural dimensions. However, these alloys have been targeted for applications, such as blades in gas-turbine engines, where relevant crack sizes are much smaller ( 5 mm) and (c ≅ 25--300 microm) cracks in a γ-TiAl based alloy, of composition Ti-47Al-2Nb-2Cr-0.2B (at.%), specifically for duplex (average grain size approximately17 microm) and refined lamellar (average colony size ≅150 microm) microstructures. It is found that, whereas the lamellar microstructure displays far superior fracture toughness and fatigue-crack growth resistance in the presence of large cracks, in small-crack testing the duplex microstructure exhibits a better combination of properties. The reasons for such contrasting behavior are examined in terms of the intrinsic and extrinsic (i.e., crack bridging) contributions to cyclic crack advance
Chen, Yunxia; Cui, Yuxuan; Gong, Wenjun
2017-01-01
Static fatigue behavior is the main failure mode of optical fibers applied in sensors. In this paper, a computational framework based on continuum damage mechanics (CDM) is presented to calculate the crack propagation process and failure time of optical fibers subjected to static bending and tensile loads. For this purpose, the static fatigue crack propagation in the glass core of the optical fiber is studied. Combining a finite element method (FEM), we use the continuum damage mechanics for the glass core to calculate the crack propagation path and corresponding failure time. In addition, three factors including bending radius, tensile force and optical fiber diameter are investigated to find their impacts on the crack propagation process and failure time of the optical fiber under concerned situations. Finally, experiments are conducted and the results verify the correctness of the simulation calculation. It is believed that the proposed method could give a straightforward description of the crack propagation path in the inner glass core. Additionally, the predicted crack propagation time of the optical fiber with different factors can provide effective suggestions for improving the long-term usage of optical fibers. PMID:29140284
Seismic behaviour of un-cracked and cracked thin pipes
International Nuclear Information System (INIS)
Blay, N.; Brunet, G.; Gantenbein, F.; Aguilar, J.
1995-01-01
In order to evaluate the seismic behaviour of un-cracked and cracked thin pipes, subjected to high acceleration levels, seismic tests and calculations have been performed on straight thin pipes made of 316L stainless steel, loaded in pure bending by a permanent static and dynamic loading. The seismic tests were carried out on the AZALEE shaking table of the CEA laboratory TAMARIS. The influence of the elasto-plastic model with isotropic or kinematic hardening are studied. 5 refs., 7 figs., 2 tabs
Nonlocal Peridynamic Modeling and Simulation on Crack Propagation in Concrete Structures
Directory of Open Access Journals (Sweden)
Dan Huang
2015-01-01
Full Text Available An extended peridynamic approach for crack propagation analysis in concrete structures was proposed. In the peridynamic constitutive model, concrete material was described as a series of interacting particles, and the short-range repulsive force and anisotropic behavior of concrete were taken into account in the expression of the interactive bonding force, which was given in terms of classical elastic constants and peridynamic horizon. The damage of material was defined locally at the level of pairwise bond, and the critical stretch of material bond was described as a function of fracture strength in the classical concrete failure theory. The efficiency and accuracy of the proposed model and algorithms were validated by simulating the propagation of mode I and I-II mixed mode cracks in concrete slabs. Furthermore, crack propagation in a double-edge notched concrete beam subjected to four-point load was simulated, in which the experimental observations are captured naturally as a consequence of the solution.
Energy Technology Data Exchange (ETDEWEB)
Ma, Longzhou
2012-11-30
The nickel-based superalloy INCONEL 617 is a candidate material for heat exchanger applications in the next-generation nuclear plant (NGNP) system. This project will study the crack propagation process of alloy 617 at temperatures of 650°C-950°C in air under static/cyclic loading conditions. The goal is to identify the environmental and mechanical damage components and to understand in-depth the failure mechanism. Researchers will measure the fatigue crack propagation (FCP) rate (da/dn) under cyclic and hold-time fatigue conditions, and sustained crack growth rates (da/dt) at elevated temperatures. The independent FCP process will be identified and the rate-controlled sustained loading crack process will be correlated with the thermal activation equation to estimate the oxygen thermal activation energy. The FCP-dependent model indicates that if the sustained loading crack growth rate, da/dt, can be correlated with the FCP rate, da/dn, at the full time dependent stage, researchers can confirm stress-accelerated grain-boundary oxygen embrittlement (SAGBOE) as a predominate effect. Following the crack propagation tests, the research team will examine the fracture surface of materials in various cracking stages using a scanning electron microscope (SEM) and an optical microscope. In particular, the microstructure of the crack tip region will be analyzed in depth using high resolution transmission electron microscopy (TEM) and electron energy loss spectrum (EELS) mapping techniques to identify oxygen penetration along the grain boundary and to examine the diffused oxygen distribution profile around the crack tip. The cracked sample will be prepared by focused ion beam nanofabrication technology, allowing researchers to accurately fabricate the TEM samples from the crack tip while minimizing artifacts. Researchers will use these microscopic and spectroscopic results to interpret the crack propagation process, as well as distinguish and understand the environment or
Evaluation of crack propagation of alloy 600 tube in high temperature water, (1)
International Nuclear Information System (INIS)
Hirano, Hideo; Kawamura, H.; Kawamura, Kohji; Matsubara, Masaaki
1990-01-01
This report describes the analysis of stress intensity factors at cracks in alloy 600 steam generator tubes. Based on the results of the analysis, IGA/SCC tests were carried out to examine the effect of stress intensity and water quality on the crack propagation rate. The main test result are as follows: (1) Hoop stress was caused by the pressure difference between the internal and external surface of the steam generator tube. The calculated hoop stress was about 7 kg/mm 2 . In addition, the temperature difference between the internal and external surface caused thermal stress. The thermal stress was about 10 kg/mm 2 at the external surface and the one at the internal surface was about -10 kg/mm 2 . Total stress at the external and internal surface was 17 kg/mm 2 and -3 kg/mm 2 , respectively. (2) The stress intensity factor at the crack tip increased with increasing crack length. For a long crack, the stress intensity factor decreased with increasing crack number. However, for a short crack, the stress intensity factor decreased little with increasing crack number. (3) Under high stress-intensity conditions, i.e. 40∼50 kg·mm -3/2 , the IGA/SCC test showed that IGA/SCC propagated in AVT and AVT/boric-acid solution at 320degC and 350degC. However, the propagation rate was low. (author)
Basic study on development of monitoring for crack propagation
International Nuclear Information System (INIS)
Enoki, Manabu; Kishi, Teruo; Kawasaki, Hirotsugu; Aoto, Kazumi
2000-03-01
The system for detecting the generation and propagation of cracks in products and materials has been investigated in this research. Firstly, in order to apply the method to harsh environment such as plant equipment, the system with laser interferometer which cables to detect fracture in non-contact way was tried. It was confirmed that the heterodyne interferometer with He-Ne laser could detect elastic waves propagating through materials, and the non-contact system with four interferometers to detect acoustic emission (AE) wave was developed. It was applied to the thermal stress fracture in alumina coating materials. AE wave during cooling of specimens due to microfracture near the interfaces was detected and the generation time, location, size and fracture mode could be evaluated by the inverse analysis. Thus, the quantitative system for evaluating AE wave was developed and the validity of this system was confirmed. Secondly, in order to predict the crack initiation, the detection tests which were performed to detect a change in damage in the pre-stage of micro crack initiation were tried. For the components that were subject to transient cyclic thermal loading changes, the ultrasonic detection test was performed, and the obtained echo was analyzed. Furthermore, the measurement of micro hardness was performed by using the micro hardness tester for the grain boundary at near crack. The ultrasound velocity which could detect damaged state before crack initiation was estimated from the wavelet analysis of ultrasonic echoes obtained here. It was confirmed to be possible to predict the crack initiation from the change of micro hardness on the grain boundary. (author)
International Nuclear Information System (INIS)
Taira, S.; Fujino, M.; Maruyama, S.
Temperature dependence of the rate of fatigue crack propagation in steels was examined, and compared with the temperature dependence of tensile ductility. Microcracks initiate and affect the propagation behavior of the main crack at elevated temperatures. Factors found to be elucidated include initiation rate of microcracks, reduction of ductility of the material in the vicinity of the main crack tip, and relaxation of concentrated strain by multi-cracks. It was found that during a strain controlled low cycle fatigue test at 1 cpm, the rate of crack propagation is largest at the blue-brittleness temperature range (200 to 300 0 C) in a low carbon steel. On the other hand, it is largest at above 700 0 C in austenite stainless steels. The temperature dependence of the rate of fatigue crack propagation is opposite to that of tensile ductility. Microcracks formed in the vicinity of the main crack tip were calculated, by considering the strain concentration and strain cycles imposed. Then, the local fracture strain was evaluated. Good correlation was found between the rate of crack propagation and the local fracture strain. (U.S.)
Prediction of three-dimensional crack propagation paths taking high cycle fatigue into account
Directory of Open Access Journals (Sweden)
Guido Dhondt
2016-01-01
Full Text Available Engine components are usually subject to complex loading patterns such as mixed-mode Low Cycle Fatigue Loading due to maneuvering. In practice, this LCF Loading has to be superimposed by High Cyclic Fatigue Loading caused by vibrations. The changes brought along by HCF are twofold: first, the vibrational cycles which are superposed on the LCF mission increase the maximum loading of the mission and may alter the principal stress planes. Secondly, the HCF cycles themselves have to be evaluated on their own, assuring that no crack propagation occurs. Indeed, the vibrational frequency is usually so high that propagation leads to immediate failure. In the present paper it is explained how these two effects can be taken care of in a standard LCF crack propagation procedure. The method is illustrated by applying the Finite Element based crack propagation software CRACKTRACER3D on an engine blade.
Fracture dynamics of a propagating crack in a pressurized ductile cylinder
International Nuclear Information System (INIS)
Emery, A.F.; Love, W.J.; Kobayashi, A.S.
1977-01-01
A suddenly-introduced axial through-crack in the wall of a pipe pressurized by hot water is allowed to propagate according to Weiss' notch-strength theory of ductile static fracture. For this somewhat ductile material of A533B steel, Weiss' criterion was extended of dynamic fracture without modification. This dynamic-fracture criterion enabled a unique comparison to be obtained for the results of ductile-fracture with those of brittle-fracture in a fracturing A533B steel pipe. Since the pipe cross-sectional area is likely to increase with large flap motions under ductile tearing, a large deformation-shell-finite-difference-dynamic-code which includes rotary inertia was used in this analysis. The uniaxial-stress-strain curve of A533B steel was approximated by a bilinear stress-strain where Von-Misses yield criterion and associated flow rule were used in the elastic-plastic analysis. The fluid pressure was assumed constant and thus pipe flaps are only lightly loaded by pressure in this analysis. In previous publications, the authors have compared their preliminary results for the shell motion obtained through their model for a fracturing pipe with those of Kanninen, et al., and Freund, et al., to evaluate the effects of pressure loading on the crack flaps and the differences between small and large deflection results. In this paper, the differences in crack-propagation behavior of a fracturing pipe composed of the same A533B but subjected to a brittle or a ductile-fracture criterion are discussed. An important conclusion in fracture dynamics derived from analyses is that a smoothly-varying crack velocity will require a non-unique crack-velocity-versus-dynamic-fracture-parameter-relation while a unique and smoothly-varying crack-velocity-versus-dynamic-fracture-parameter-relation will demand an intermittently-propagating crack
Crack propagation and acoustic emission behavior of silver-added Dy123 bulk superconductor
International Nuclear Information System (INIS)
Yoneda, K.; Ye, J.
2006-01-01
The relationship between the crack propagation process and acoustic emission (AE) signals was investigated in 3-point bending tests in which stress loading was applied parallel to the c-axis of U-notched specimens cut from Dy123 bulk superconductors with and without the addition of silver (Ag). The average bending stress of the specimens containing 10 mass% of Ag was approximately 20% higher than that of the specimens without the addition of Ag; the total AE energy of the former specimens was approximately fourfold greater than that of the latter specimens. However, cracks initiated in all of the specimens at a bending stress level of around 25 MPa, regardless of the presence or absence of Ag. An analysis of the amplitude distribution revealed that the failure mode was matrix failure in both types of specimens. Cracks in the low-strength specimens without Ag propagated between gas holes or along cleavage planes, and the AE event count and total AE energy were low. By contrast, the high-strength Ag-added specimens had fewer gas holes and cleavage cracks on account of their improved microstructure. In these samples, crack propagation orthogonal to the cleavage planes caused Ag particles to separate from the matrix and induced cleavage cracks. The addition of Ag presumably had the effect of inhibiting crack propagation, with the result that the AE event count and AE energy increased. The results of this study indicate that failure phenomena can be interpreted by evaluating the amplitude distribution, AE event count and total AE energy. This suggests that the AE method is also applicable to evaluations of bulk superconductors
Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)
DEFF Research Database (Denmark)
Paegle, Ieva; Fischer, Gregor
2011-01-01
Knowledge of the mechanisms controlling crack formation, propagation and failure of FRCC under shear loading is currently limited. This paper presents a study that utilized photogrammetry to monitor the shear deformations of two FRCC materials and ordinary concrete (OC). Multiple shear cracks...... and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...
Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)
DEFF Research Database (Denmark)
Paegle, Ieva; Fischer, Gregor
2012-01-01
Knowledge of the mechanisms controlling crack formation, propagation and failure of FRCC under shear loading is currently limited. This paper presents a study that utilized photogrammetry to monitor the shear deformations of two FRCC materials and ordinary concrete (OC). Multiple shear cracks...... and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...
Radiation efficiency during slow crack propagation: an experimental study.
Jestin, Camille; Lengliné, Olivier; Schmittbuhl, Jean
2017-04-01
Creeping faults are known to host a significant aseismic deformation. However, the observations of micro-earthquake activity related to creeping faults (e.g. San Andreas Faults, North Anatolian Fault) suggest the presence of strong lateral variabilities of the energy partitioning between radiated and fracture energies. The seismic over aseismic slip ratio is rather difficult to image over time and at depth because of observational limitations (spatial resolution, sufficiently broad band instruments, etc.). In this study, we aim to capture in great details the energy partitioning during the slow propagation of mode I fracture along a heterogeneous interface, where the toughness is strongly varying in space.We lead experiments at laboratory scale on a rock analog model (PMMA) enabling a precise monitoring of fracture pinning and depinning on local asperities in the brittle-creep regime. Indeed, optical imaging through the transparent material allows the high resolution description of the fracture front position and velocity during its propagation. At the same time, acoustic emissions are also measured by accelerometers positioned around the rupture. Combining acoustic records, measurements of the crack front position and the loading curve, we compute the total radiated energy and the fracture energy. We deduce from them the radiation efficiency, ηR, characterizing the proportion of the available energy that is radiated in form of seismic wave. We show an increase of ηR with the crack rupture speed computed for each of our experiments in the sub-critical crack propagation domain. Our experimental estimates of ηR are larger than the theoretical model proposed by Freund, stating that the radiation efficiency of crack propagation in homogeneous media is proportional to the crack velocity. Our results are demonstrated to be in agreement with existing studies which showed that the distribution of crack front velocity in a heterogeneous medium can be well described by a
International Nuclear Information System (INIS)
Dumouchel, P.E.
2008-03-01
This research thesis aims at understanding and analysing some mechanisms involved in the dynamic failure under various loadings which are notably present in industrial environment, and more particularly in some parts of EDF's plants where networks of micro-cracks may steadily grow: heterogeneous zones, defects under coating. The author presents a simplified model based on the de-bonding of a film to understand the mechanisms of a sudden failure under a quasi-static loading. He develops a similar model to explore the influence of a defect on crack propagation under a quasi-static loading, and then under a sudden loading. This model is then generalized to the case of several defects, and more particularly very small defects. Finally, the author gives a numerical interpretation of a sudden propagation under quasi-static loading
Time-dependent corrosion fatique crack propagation in 7000 series aluminum alloys. M.S. Thesis
Mason, Mark E.
1995-01-01
The goal of this research is to characterize environmentally assisted subcritical crack growth for the susceptible short-longitudinal orientation of aluminum alloy 7075-T651, immersed in acidified and inhibited NaCl solution. This work is necessary in order to provide a basis for incorporating environmental effects into fatigue crack propagation life prediction codes such as NASA-FLAGRO (NASGRO). This effort concentrates on determining relevant inputs to a superposition model in order to more accurately model environmental fatigue crack propagation.
Experimental and numerical modelling of ductile crack propagation in large-scale shell structures
DEFF Research Database (Denmark)
Simonsen, Bo Cerup; Törnquist, R.
2004-01-01
plastic and controlled conditions. The test specimen can be deformed either in combined in-plane bending and extension or in pure extension. Experimental results are described for 5 and 10 mm thick aluminium and steel plates. By performing an inverse finite-element analysis of the experimental results......This paper presents a combined experimental-numerical procedure for development and calibration of macroscopic crack propagation criteria in large-scale shell structures. A novel experimental set-up is described in which a mode-I crack can be driven 400 mm through a 20(+) mm thick plate under fully...... for steel and aluminium plates, mainly as curves showing the critical element deformation versus the shell element size. These derived crack propagation criteria are then validated against a separate set of experiments considering centre crack specimens (CCS) which have a different crack-tip constraint...
Study of fatigue crack propagation in laminated metal composites alluminium 1100/alluminium 2024
International Nuclear Information System (INIS)
Tavares, R.I.
1984-01-01
A study has been made of fatigue crack propagation in laminated metal composites with different volume fraction of constituents. The composites were produced by hot rolling, combining 1100 and 2024 aluminum alloys in crack divider orientation. Mechanical and metallurgical properties of the composites and original alloys sheets have been evaluated. Paris type relationship, corresponding to stage II of fatigue crack propagation curves, has been determined by two different methods, wich have shown to be equivalent. A computer software in FORTRAN language was developed for all the mathematical manipulation of fatigue data including statistical analysis and graphics. (Author) [pt
International Nuclear Information System (INIS)
Martins, Geraldo de Paula; Cimini Junior, Carlos Alberto; Godefroid, Leonardo Barbosa
2005-01-01
The welding process introduces defects on the welded joints, as lack of fusion and penetration, porosity, between others. These defects can compromise the structures or components, relative to the crack propagation. This engagement can be studied by fatigue crack propagation tests. The efficiency of the structure, when submitted to a cyclic loading can be evaluated by these tests. The aim of this work is to study the behavior of welded joints containing defects as lack of penetration at the root or between welding passes relative to crack propagation resistance properties, and to compare these properties with the properties of the welded joints without defects. This study was accomplished from fatigue crack propagation test results, in specimens containing lack of penetration between welding passes. With the obtained results, the Paris equation coefficients and exponents that relate the crack propagation rate with the stress intensity cyclic factor for welded joints with and without defects were obtained. (author)
Energy Technology Data Exchange (ETDEWEB)
Min, Zhang [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Xi-ping, Song, E-mail: xpsong@skl.ustb.edu.cn [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Long, Yu; Hong-liang, Li [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Ze-hui, Jiao; Hui-chen, Yu [National Key Laboratory of Science and Technology on Advanced High Temperature Structural Materials, Beijing Institute of Aeronautical Materials, Beijing 100095 (China)
2015-01-12
In this paper, the fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy with nearly lamellar microstructure was studied by in situ scanning electron microscope observation at 750 °C. Dog-bone shaped specimens with a single-edge notch were used in the test. The results showed that the fatigue crack initiated first at the central portion of the notch, and then shifted to the edge portion. As the cycle numbers went on increasing, these cracks joined together and formed a main fatigue crack, which could propagate along the surface of the specimen. During the fatigue crack propagation two or three propagation stages were found depending on the microstructure of the crack tip. When the fatigue crack was parallel to the lamellar laths, it exhibited the rapid, steady and accelerated propagation stages successively, while when the fatigue crack was perpendicular to the lamellar laths, it exhibited only the steady and accelerated propagation stages, with no rapid propagation stage being found. In these different propagation stages the fatigue crack propagation rates were different and depended intensively on the lamellar laths orientation, lamellar colony size, equiaxed gamma grains and peak stress intensity factor K{sub max}. Based on the experimental data it was concluded that the fatigue crack initiation lifetime was much longer than the propagation lifetime for the single-edge notched specimens at 750 °C.
International Nuclear Information System (INIS)
Min, Zhang; Xi-ping, Song; Long, Yu; Hong-liang, Li; Ze-hui, Jiao; Hui-chen, Yu
2015-01-01
In this paper, the fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy with nearly lamellar microstructure was studied by in situ scanning electron microscope observation at 750 °C. Dog-bone shaped specimens with a single-edge notch were used in the test. The results showed that the fatigue crack initiated first at the central portion of the notch, and then shifted to the edge portion. As the cycle numbers went on increasing, these cracks joined together and formed a main fatigue crack, which could propagate along the surface of the specimen. During the fatigue crack propagation two or three propagation stages were found depending on the microstructure of the crack tip. When the fatigue crack was parallel to the lamellar laths, it exhibited the rapid, steady and accelerated propagation stages successively, while when the fatigue crack was perpendicular to the lamellar laths, it exhibited only the steady and accelerated propagation stages, with no rapid propagation stage being found. In these different propagation stages the fatigue crack propagation rates were different and depended intensively on the lamellar laths orientation, lamellar colony size, equiaxed gamma grains and peak stress intensity factor K max . Based on the experimental data it was concluded that the fatigue crack initiation lifetime was much longer than the propagation lifetime for the single-edge notched specimens at 750 °C
Diffraction-based study of fatigue crack initiation and propagation in aerospace aluminum alloys
Gupta, Vipul K.
The crack initiation sites and microstructure-sensitive growth of small fatigue cracks are experimentally characterized in two precipitation-hardened aluminum alloys, 7075-T651 and 7050-T7451, stressed in ambient temperature moist-air (warm-humid) and -50°C dry N2 (cold-dry) environmental conditions. Backscattered electron imaging (BSE) and energy dispersive spectroscopy (EDS) of the fracture surfaces showed that Fe-Cu rich constituent particle clusters are the most common initiation sites within both alloys stressed in either environment. The crack growth within each alloy, on average, was observed to be slowed in the cold-dry environment than in the warm-humid environment, but only at longer crack lengths. Although no overwhelming effects of grain boundaries and grain orientations on small-crack growth were observed, crack growth data showed local fluctuations within individual grains. These observations are understood as crack propagation through the underlying substructure at the crack surface and frequent interaction with low/high-angle grain and subgrain boundaries, during cyclic loading, and, are further attributed to periodic changes in crack propagation path and multiple occurrences of crack-branching observed in the current study. SEM-based stereology in combination with electron backscattered diffraction (EBSD) established fatigue crack surface crystallography within the region from ˜1 to 50 mum of crack initiating particle clusters. Fatigue crack facets were parallel to a wide variety of crystallographic planes, with pole orientations distributed broadly across the irreducible stereographic triangle between the {001} and {101}-poles within both warm-humid and cold-dry environments. The results indicate environmentally affected fatigue cracking in both cases, given the similarity between the observed morphology and crystallography with that of a variety of aerospace aluminum alloys cracked in the presence of moist-air. There was no evidence of
Near-threshold fatigue crack behaviour in EUROFER 97 at different temperatures
Aktaa, J.; Lerch, M.
2006-07-01
The fatigue crack behaviour in EUROFER 97 was investigated at room temperature (RT), 300, 500 and 550 °C for the assessment of cracks in first wall structures built from EUROFER 97 of future fusion reactors. For this purpose, fatigue crack growth tests were performed using CT specimens with two R-ratios, R = 0.1 and R = 0.5 ( R is the load ratio with R = Fmin/ Fmax where Fmin and Fmax are the minimum and maximum applied loads within a cycle, respectively). Hence, fatigue crack threshold, fatigue crack growth behaviour in the near-threshold range and their dependences on temperature and R-ratio were determined and described using an analytical formula. The fatigue crack threshold showed a monotonous dependence on temperature which is for R = 0.5 insignificantly small. The fatigue crack growth behaviour exhibited for R = 0.1 a non-monotonous dependence on temperature which is explained by the decrease of yield stress and the increase of creep damage with increasing temperature.
A methodology for the investigation of toughness and crack propagation in mouse bone.
Carriero, Alessandra; Zimmermann, Elizabeth A; Shefelbine, Sandra J; Ritchie, Robert O
2014-11-01
Bone fracture is a health concern for those with aged bone and brittle bone diseases. Mouse bone is widely used as a model of human bone, especially to investigate preclinical treatment strategies. However, little is known about the mechanisms of mouse bone fracture and its similarities and differences from fracture in human bone. In this work we present a methodology to investigate the fracture toughness during crack initiation and crack propagation for mouse bone. Mouse femora were dissected, polished on their periosteal surface, notched on the posterior surface at their mid-diaphysis, and tested in three-point bending under displacement control at a rate of 0.1mm/min using an in situ loading stage within an environmental scanning electron microscope. We obtained high-resolution real-time imaging of the crack initiation and propagation in mouse bone. From the images we can measure the crack extension at each step of the crack growth and calculate the toughness of the bone (in terms of stress intensity factor (K) and work to fracture (Wf)) as a function of stable crack length (Δa), thus generating a resistance curve for the mouse bone. The technique presented here provides insight into the evolution of microdamage and the toughening mechanisms that resist crack propagation, which are essential for preclinical development of treatments to enhance bone quality and combat fracture risk. Copyright © 2014 Elsevier Ltd. All rights reserved.
Shear crack formation and propagation in reinforced Engineered Cementitious Composites
DEFF Research Database (Denmark)
Paegle, Ieva; Fischer, Gregor
2011-01-01
capacity of beams loaded primarily in shear. The experimental program consists of ECC with short randomly distributed polyvinyl alcohol (PVA) fiber beams with different stirrup arrangements and conventional reinforced concrete (R/C) counterparts for comparison. The shear crack formation mechanism of ECC......This paper describes an experimental investigation of the shear behaviour of beams consisting of steel reinforced Engineered Cementitious Composites (R/ECC). Based on the strain hardening and multiple cracking behaviour of ECC, this study investigates the extent to which ECC influences the shear...
Threshold intensity factors as lower boundaries for crack propagation in ceramics
Directory of Open Access Journals (Sweden)
Walter Per-Ole
2004-11-01
Full Text Available Abstract Background Slow crack growth can be described in a v (crack velocity versus KI (stress intensity factor diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip induces crack propagation, which eventually may result in fatigue. The presence of a threshold in the stress intensity factor, below which no crack propagation occurs, has been the subject of important research in the last years. The higher this threshold, the higher the reliability of the ceramic, and consequently the longer its lifetime. Methods We utilize the Irwin K-field displacement relation to deduce crack tip stress intensity factors from the near crack tip profile. Cracks are initiated by indentation impressions. The threshold stress intensity factor is determined as the time limit of the tip stress intensity when the residual stresses have (nearly disappeared. Results We determined the threshold stress intensity factors for most of the all ceramic materials presently important for dental restorations in Europe. Of special significance is the finding that alumina ceramic has a threshold limit nearly identical with that of zirconia. Conclusion The intention of the present paper is to stress the point that the threshold stress intensity factor represents a more intrinsic property for a given ceramic material than the widely used toughness (bend strength or fracture toughness, which refers only to fast crack growth. Considering two ceramics with identical threshold limits, although with different critical stress intensity limits, means that both ceramics have identical starting points for slow crack growth. Fast catastrophic crack growth leading to spontaneous fatigue, however, is different. This growth starts later in those ceramic materials
3D dynamic simulation of crack propagation in extracorporeal shock wave lithotripsy
Wijerathne, M. L. L.; Hori, Muneo; Sakaguchi, Hide; Oguni, Kenji
2010-06-01
Some experimental observations of Shock Wave Lithotripsy(SWL), which include 3D dynamic crack propagation, are simulated with the aim of reproducing fragmentation of kidney stones with SWL. Extracorporeal shock wave lithotripsy (ESWL) is the fragmentation of kidney stones by focusing an ultrasonic pressure pulse onto the stones. 3D models with fine discretization are used to accurately capture the high amplitude shear shock waves. For solving the resulting large scale dynamic crack propagation problem, PDS-FEM is used; it provides numerically efficient failure treatments. With a distributed memory parallel code of PDS-FEM, experimentally observed 3D photoelastic images of transient stress waves and crack patterns in cylindrical samples are successfully reproduced. The numerical crack patterns are in good agreement with the experimental ones, quantitatively. The results shows that the high amplitude shear waves induced in solid, by the lithotriptor generated shock wave, play a dominant role in stone fragmentation.
Research on a Lamb Wave and Particle Filter-Based On-Line Crack Propagation Prognosis Method
Chen, Jian; Yuan, Shenfang; Qiu, Lei; Cai, Jian; Yang, Weibo
2016-01-01
Prognostics and health management techniques have drawn widespread attention due to their ability to facilitate maintenance activities based on need. On-line prognosis of fatigue crack propagation can offer information for optimizing operation and maintenance strategies in real-time. This paper proposes a Lamb wave-particle filter (LW-PF)-based method for on-line prognosis of fatigue crack propagation which takes advantages of the possibility of on-line monitoring to evaluate the actual crack...
Combined simulation of fatigue crack nucleation and propagation based on a damage indicator
Directory of Open Access Journals (Sweden)
M. Springer
2016-10-01
Full Text Available Fatigue considerations often distinguish between fatigue crack nucleation and fatigue crack propagation. The current work presents a modeling approach utilizing one Fatigue Damage Indicator to treat both in a unified way. The approach is implemented within the framework of the Finite Element Method. Multiaxial critical plane models with an extended damage accumulation are employed as Fatigue Indicators. Locations of fatigue crack emergence are predicted by these indicators and material degradation is utilized to model local material failure. The cyclic loading is continued on the now degraded structure and the next location prone to material failure is identified and degradation modeled. This way, fatigue crack propagation is represented by an evolving spatial zone of material failure. This propagating damage zone leads to a changing structural response of the pristine structure. By recourse to the Fatigue Damage Indicator a correlation between the number of applied load cycles and the changing structural behavior is established. Finally, the proposed approach is exemplified by cyclic bending experiments in the Low Cycle Fatigue regime
International Nuclear Information System (INIS)
Torii, Tashiyuki; Toi, Norihiko; Nakano, Kohji; Honda, Kazuo
1998-01-01
Using the X-ray method of stress measurement for Ti-6Al-4V alloys, the residual stress near the crack was measured for annealed (AN) and solution treated and aged (STA) titanium alloys, under the condition that the measured X-ray stress was in satisfactory agreement with the applied stress under tension. The residual stress measured in the wake of the propagating fatigue crack, σ r , was compressive, resulting in a smaller crack opening displacement, COD, than theorized. The measured σ r and COD-values let us understand the fatigue crack propagation rate da/dN in terms of the effective stress intensity factor K eff . As a result, the da/dN under the same K eff -value was smaller in the AN specimen with zigzag crack growth than in the STA specimen with straight crack growth, although the da/dN-K eff relationship under various stress amplitudes was represented by a straight line in a log-log scale separately for the AN and STA specimens. (author)
Energy Technology Data Exchange (ETDEWEB)
Martins, Geraldo de Paula; Villela, Jefferson Jose; Rabello, Emerson Giovani [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)]. E-mails: gpm@cdtn.br; jjv@cdtn.br; egr@cdtn.br; Cimini Junior, Carlos Alberto[Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Dept. de Engenharia Mecanica]. E-mail: cimini@demet.ufmg.br; Godefroid, Leonardo Barbosa [Universidade Federal de Ouro Preto (UFOP), MG (Brazil). Dept. de Metalurgia]. E-mails: leonardo@demet.em.ufop.br
2007-07-01
In this work, the influence of stress relieve heat treatment (SRHT) on the fatigue crack propagation in USI-SAC 50 structural welded joints at the heat affected zone (HAZ) region was studied. Hardness measurements before and after the SRHT were made and crack propagation tests in specimens as welded (AW) and in specimens that were submitted to SRHT, which were accomplished. A reduction in hardness at the regions of HAZ and melted zone (MZ) after the SRHT were observed. It were also verified that the crack propagation rates (da/dN) versus DK on the specimens AW presented regions of retardation on the crack propagation rate, and in the specimens that were submitted to SRHT the crack propagation rate were homogeneous. (author)
Jingjing, Zheng; Tiezhou, Hou; Hong, Tao; Xueyan, Guo; Cui, Wu
2014-10-01
This study aims to identify the crack tip stress intensity factor of the propagation process, crack propagation path, and the changes in the shape of the crack tip by the finite element method. The finite element model of dentino-enamel junction was established with ANSYS software, and the length of the initial crack in the single edge was set to 0.1 mm. The lower end of the sample was fixed. The tensile load of 1 MPa with frequency of 5 Hz was applied to the upper end. The stress intensity factor, deflection angle, and changes in the shape of the crack tip in the crack propagation were calculated by ANSYS. The stress intensity factor suddenly and continuously decreased in dentino-enamel junction as the crack extended. A large skewed angle appeared, and the stress on crack tip was reduced. The dentino-enamel junction on human teeth may resist crack propagation through stress reduction.
Energy Technology Data Exchange (ETDEWEB)
Kubo, T., E-mail: kubo@nfd.co.jp [Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Ibaraki 311-1313 (Japan); Kobayashi, Y. [M.O.X. Co., Ltd., 1828-520 Hirasu-cho, Mito, Ibaraki 311-0853 (Japan); Uchikoshi, H. [Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Ibaraki 311-1313 (Japan)
2012-08-15
Highlights: Black-Right-Pointing-Pointer The delayed hydride cracking (DHC) velocity of Zircaloy-2 was measured. Black-Right-Pointing-Pointer The velocity followed the Arrhenius law up to 270 Degree-Sign C. Activation energy was 49 kJ/mol. Black-Right-Pointing-Pointer The threshold stress intensity factor for the DHC was from 4 to 6 MPa m{sup 1/2}. Black-Right-Pointing-Pointer An increase in material strength accelerated the DHC. Black-Right-Pointing-Pointer Precipitation and fracture of hydrides at a crack tip is responsible for the DHC. - Abstract: Delayed hydride cracking (DHC) tests of Zircaloy-2 cladding tubes were performed in the chamber of a scanning electron microscope (SEM) to directly observe the crack propagation and measure the crack velocity in the radial direction of the tubes. Pre-cracks were produced at the outer surfaces of the tubes. Hydrogen contents of the tubes were from 90 ppm to 130 ppm and test temperatures were from 225 Degree-Sign C to 300 Degree-Sign C. The crack velocity followed the Arrhenius law at temperatures lower than about 270 Degree-Sign C with apparent activation energy of about 49 kJ/mol. The upper temperature limit for DHC, above which DHC did not occur, was about 280 Degree-Sign C. The threshold stress intensity factor for the initiation of the crack propagation, K{sub IH}, was from about 4 MPa m{sup 1/2} to 6 MPa m{sup 1/2}, almost independent of temperature. An increase in 0.2% offset yield stress of the material accelerated the crack velocity and slightly decreased K{sub IH}. Detailed observations of crack tip movement showed that cracks propagated in an intermittent fashion and the propagation gradually approached the steady state as the crack depth increased. The SEM observations also showed that hydrides were formed at a crack tip and a number of micro-cracks were found in the hydrides. It was presumed from these observations that the repetition of precipitation and fracture of hydrides at the crack tip would be
Fatigue crack Behaviour in a High Strength Tool Steel
DEFF Research Database (Denmark)
Højerslev, Christian; Carstensen, Jesper V.; Brøndsted, Povl
2002-01-01
The influence of microstructure on fatigue crack initiation and crack growth of a hardened and tempered high speed steel was investigated. The evolution of fatigue cracks was followed in four point bending at room temperature. It was found that a carbide damage zone exists above a threshold load...... value of maximally 80% of the yield strength of the steel. The size of this carbide damage zone increases with increasing load amplitude, and the zone is apparently associated with crack nucleation. On fatigue crack propagation plastic deformation of the matrix occurs in a radius of approximately 4...... microns in front of the fatigue crack tip, which is comparable with the relevant mean free carbide spacing....
International Nuclear Information System (INIS)
Sato, Yasumoto; Atsumi, Takeo; Shoji, Tetsuo
2006-01-01
In order to investigate the applicability of the potential drop techniques to the continuous monitoring of stress corrosion cracking (SCC) propagation, SCC tests were performed in a sodium thiosulfate solution at room temperature using plate specimens with weldments. The SCC propagation was monitored using the techniques of direct current potential drop (DCPD), alternating current potential drop (ACPD) and modified induced current potential drop (MICPD) on the reverse side that on which the SCC existed and effectiveness of each technique for the continuous monitoring from the reverse side of SCC was compared from the viewpoints of sensitivity to the crack propagation and measurement stability. The MICPD and DCPD techniques permit continuous monitoring of the back-wall SCC propagation, which initiates from a fatigue pre-crack at a depth of about 4 mm, from which it propagates through more than 80% of the specimen thickness. The MICPD technique can decrease the effect of the current flowing in the direction of the crack length by focusing the induced current into the local area of measurement using induction coils, so that the sensitivity of the continuous monitoring of the back wall SCC propagation is higher than that of the DCPD and ACPD techniques. (author)
Directory of Open Access Journals (Sweden)
Luiz Carlos H. Ricardo
2016-03-01
Full Text Available Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique as criterion design. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FD&E SAE Keyhole Specimen Test Load Histories by finite element analysis. The crack propagation simulation was based on release nodes at the minimum loads to minimize convergence problems. To understand the crack propagation processes under variable amplitude loading, retardation effects are discussed.
Hydrogen induced crack propagation in metal under plain-strain deformation
International Nuclear Information System (INIS)
Fishgojt, A.V.; Kolachev, B.A.
1981-01-01
A model of subcritical crack propagation conditioned by the effect of dissolved hydrogen in the case of plane-strain deformation of high-strength materials, is suggested. It is supposed that diffusion takes place in the isotropic material and hydrogen diffuses in the region of tensile stress maximum before crack tip under the effect of the stress gradient. When hydrogen achieves the critical concentration, microcrack growth takes place. Values of crack growth rates experimentally obtained agree with values calculated according to the suggested formula. Calculation and experimental data on the Ti-6Al-4V alloy, are presented [ru
Fatigue crack propagation behavior of stainless steel welds
Kusko, Chad S.
The fatigue crack propagation behavior of austenitic and duplex stainless steel base and weld metals has been investigated using various fatigue crack growth test procedures, ferrite measurement techniques, light optical microscopy, stereomicroscopy, scanning electron microscopy, and optical profilometry. The compliance offset method has been incorporated to measure crack closure during testing in order to determine a stress ratio at which such closure is overcome. Based on this method, an empirically determined stress ratio of 0.60 has been shown to be very successful in overcoming crack closure for all da/dN for gas metal arc and laser welds. This empirically-determined stress ratio of 0.60 has been applied to testing of stainless steel base metal and weld metal to understand the influence of microstructure. Regarding the base metal investigation, for 316L and AL6XN base metals, grain size and grain plus twin size have been shown to influence resulting crack growth behavior. The cyclic plastic zone size model has been applied to accurately model crack growth behavior for austenitic stainless steels when the average grain plus twin size is considered. Additionally, the effect of the tortuous crack paths observed for the larger grain size base metals can be explained by a literature model for crack deflection. Constant Delta K testing has been used to characterize the crack growth behavior across various regions of the gas metal arc and laser welds at the empirically determined stress ratio of 0.60. Despite an extensive range of stainless steel weld metal FN and delta-ferrite morphologies, neither delta-ferrite morphology significantly influence the room temperature crack growth behavior. However, variations in weld metal da/dN can be explained by local surface roughness resulting from large columnar grains and tortuous crack paths in the weld metal.
Near-threshold fatigue crack behaviour in EUROFER 97 at different temperatures
International Nuclear Information System (INIS)
Aktaa, J.; Lerch, M.
2006-01-01
The fatigue crack behaviour in EUROFER 97 was investigated at room temperature (RT), 300, 500 and 550 deg. C for the assessment of cracks in first wall structures built from EUROFER 97 of future fusion reactors. For this purpose, fatigue crack growth tests were performed using CT specimens with two R-ratios, R = 0.1 and R = 0.5 (R is the load ratio with R = F min /F max where F min and F max are the minimum and maximum applied loads within a cycle, respectively). Hence, fatigue crack threshold, fatigue crack growth behaviour in the near-threshold range and their dependences on temperature and R-ratio were determined and described using an analytical formula. The fatigue crack threshold showed a monotonous dependence on temperature which is for R = 0.5 insignificantly small. The fatigue crack growth behaviour exhibited for R = 0.1 a non-monotonous dependence on temperature which is explained by the decrease of yield stress and the increase of creep damage with increasing temperature
Energy Technology Data Exchange (ETDEWEB)
Jeong, Dae-Ho [Department of Materials Science and Engineering, RECAPT, Gyeongsang National University, Chinju (Korea, Republic of); Choi, Myung-Je [Korea Aerospace Industry, Sacheon (Korea, Republic of); Goto, Masahiro [Department of Mechanical Engineering, Oita University, Oita (Japan); Lee, Hong-Chul [Republic of Korea Air Force (Korea, Republic of); Kim, Sangshik, E-mail: sang@gnu.ac.kr [Department of Materials Science and Engineering, RECAPT, Gyeongsang National University, Chinju (Korea, Republic of)
2014-09-15
In this study, the fatigue crack propagation behavior of Inconel 718 turbine disc with different service times from 0 to 4229 h was investigated at 738 and 823 K. No notable change in microstructural features, other than the increase in grain size, was observed with increasing service time. With increasing service time from 0 to 4229 h, the fatigue crack propagation rates tended to increase, while the ΔK{sub th} value decreased, in low ΔK regime and lower Paris' regime at both testing temperatures. The fractographic observation using a scanning electron microscope suggested that the elevated temperature fatigue crack propagation mechanism of Inconel 718 changed from crystallographic cleavage mechanism to striation mechanism in the low ΔK regime, depending on the grain size. The fatigue crack propagation mechanism is proposed for the crack propagating through small and large grains in the low ΔK regime, and the fatigue crack propagation behavior of Inconel 718 with different service times at elevated temperatures is discussed. - Highlights: • The specimens were prepared from the Inconel 718 turbine disc used for 0 to 4229 h. • FCP rates were measured at 738 and 823 K. • The ΔK{sub th} values decreased with increasing service time. • The FCP behavior showed a strong correlation with the grain size of used turbine disc.
International Nuclear Information System (INIS)
Bongue Boma, M.
2007-12-01
We propose a model describing the evolution of mechanical and permeability properties of concrete under slow mechanical loading. Calling upon the theory of continua with microstructure, the kinematic of the domain is enriched by a variable characterising size and orientation of the crack field. We call upon configurational forces to deal with crack propagation and we determine the balance equations governing both strain and propagation. The geometry of the microstructure is representative of the porous media: the permeability is obtained from the resolution of Stokes equations in an elementary volume. An example has been treated: we considered simple assumptions (uniform crack field, application of linear fracture mechanics...) and we determined the behaviour of a body under tensile loading. Strain, crack propagation and stiffness loss are completely assessed. Finally the evolution of permeability is plotted: once activated, crack propagation is the main cause of water tightness loss. (author)
International Nuclear Information System (INIS)
Chen, A.Y.; Li, D.F.; Zhang, J.B.; Liu, F.; Liu, X.R.; Lu, J.
2011-01-01
Highlights: → A nanostructured and layered steel exhibits high strength and large ductility. → The excellent combination originates from a multiple interlaminar cracking. → The initiation and propagation of cracks are controlled by three aspects. → The cracks are deflected by interface and arrested by compressive residual stress. → Finally, the cracks are blunted by the graded grain size distribution. - Abstract: A layered and nanostructured (LN) 304 SS sheet was produced by combination of surface mechanical attrition treatment (SMAT) with warm co-rolling. The microstructure of LN sheet is characterized by a periodic distribution of nanocrystalline layers and micron-grained layers with a graded transition of grain size. Tensile test results show that exceptional properties of high yield strength and large elongation to fracture are achieved. A multiple interlaminar cracking was observed by scanning electron microscopy, which is induced by repeated crack initiation and propagation. The toughening mechanisms of the LN sheet are proposed to be controlling the crack propagation path by several strategies. The main cracks initiating at interface defects are arrested by large compressive residual stress, deflected by weak interface bonding and blunted by the graded grain size distribution.
Directory of Open Access Journals (Sweden)
Yongshui Kang
2014-10-01
Full Text Available Water-bearing rocks exposed to freezing temperature can be subjected to freeze–thaw cycles leading to crack initiation and propagation, which are the main causes of frost damage to rocks. Based on the Griffith theory of brittle fracture mechanics, the crack initiation criterion, propagation direction, and crack length under freezing pressure and far-field stress are analyzed. Furthermore, a calculation method is proposed for the stress intensity factor (SIF of the crack tip under non-uniformly distributed freezing pressure. The formulae for the crack/fracture propagation direction and length of the wing crack under freezing pressure are obtained, and the mechanism for coalescence of adjacent cracks is investigated. In addition, the necessary conditions for different coalescence modes of cracks are studied. Using the topology theory, a new algorithm for frost crack propagation is proposed, which has the capability to define the crack growth path and identify and update the cracked elements. A model that incorporates multiple cracks is built by ANSYS and then imported into FLAC3D. The SIFs are then calculated using a FISH procedure, and the growth path of the freezing cracks after several calculation steps is demonstrated using the new algorithm. The proposed method can be applied to rocks containing fillings such as detritus and slurry.
Directory of Open Access Journals (Sweden)
G. M. Domínguez Almaraz
2015-10-01
Full Text Available Crack initiation and propagation have been investigated on the polymeric material ABS (Acrylonitrile Butadiene Styrene, under ultrasonic fatigue testing. Three controlled actions were implemented in order to carry out fatigue tests at very high frequency on this material of low thermal conductivity, they are: a The applying load was low to limit heat dissipation at the specimen neck section, b The dimensions of testing specimen were small (but fitting the resonance condition, in order to restraint the temperature gradient at the specimen narrow section, c Temperature at the specimen neck section was restrained by immersion in water or oil during ultrasonic fatigue testing. Experimental results are discussed on the basis of thermo-mechanical behaviour: the tail phenomenon at the initial stage of fatigue, initial shear yielding deformation, crazed development on the later stage, plastic strain on the fracture surface and the transition from low to high crack growth rate. In addition, a numerical analysis is developed to evaluate the J integral of energy dissipation and the stress intensity factor K, with the crack length
Effects of friction and high torque on fatigue crack propagation in Mode III
Nayeb-Hashemi, H.; McClintock, F. A.; Ritchie, R. O.
1982-12-01
Turbo-generator and automotive shafts are often subjected to complex histories of high torques. To provide a basis for fatigue life estimation in such components, a study of fatigue crack propagation in Mode III (anti-plane shear) for a mill-annealed AISI 4140 steel (RB88, 590 MN/m2 tensile strength) has been undertaken, using torsionally-loaded, circumferentially-notched cylindrical specimens. As demonstrated previously for higher strength AISI 4340 steel, Mode III cyclic crack growth rates (dc/dN) IIIcan be related to the alternating stress intensity factor ΔKIII for conditions of small-scale yielding. However, to describe crack propagation behavior over an extended range of crack growth rates (˜10-6 to 10-2 mm per cycle), where crack growth proceeds under elastic-plastic and full plastic conditions, no correlation between (dc/dN) III and ΔKIII is possible. Accordingly, a new parameter for torsional crack growth, termed the plastic strain intensity Γ III, is introduced and is shown to provide a unique description of Mode III crack growth behavior for a wide range of testing conditions, provided a mean load reduces friction, abrasion, and interlocking between mating fracture surfaces. The latter effect is found to be dependent upon the mode of applied loading (i.e., the presence of superimposed axial loads) and the crack length and torque level. Mechanistically, high-torque surfaces were transverse, macroscopically flat, and smeared. Lower torques showed additional axial cracks (longitudinal shear cracking) perpendicular to the main transverse surface. A micro-mechanical model for the main radi l Mode III growth, based on the premise that crack advance results from Mode II coalescence of microcracks initiated at inclusions ahead of the main crack front, is extended to high nominal stress levels, and predicts that Mode III fatigue crack propagation rates should be proportional to the range of plastic strain intensity (ΔΓIII if local Mode II growth rates are
Dynamic crack propagation through nanoporous media
Nguyen, Thao; Wilkerson, Justin
2015-06-01
The deformation and failure of nanoporous metals may be considerably different than that of more traditional bulk porous metals. The length scales in traditional bulk porous metals are typically large enough for classic plasticity and buckling to be operative. However, the extremely small length scales associated with nanoporous metals may inhibit classic plasticity mechanisms. Here, we motivate an alternative nanovoid growth mechanism mediated by dislocation emission. Following an approach similar to Lubarda and co-workers, we make use of stability arguments applied to the analytic solutions of the elastic interactions of dislocations and voids to derive a simple stress-based criterion for emission activation. We then propose a dynamic nanovoid growth law that is motivated by the kinetics of dislocation emission. The resulting failure model is implemented into a commercial finite element software to simulate dynamic crack growth. The simulations reveal that crack propagation through a nanoporous media proceeds at somewhat faster velocities than through the more traditional bulk porous metal.
Effect of segregations on mechanical properties and crack propagation in spring steel
Directory of Open Access Journals (Sweden)
B. Žužek
2015-10-01
Full Text Available Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel.
International Nuclear Information System (INIS)
Huang, H.Y.; Chu, W.Y.; Su, Y.J.; Qiao, L.J.; Gao, K.W.
2005-01-01
The combined effect of electric field and residual stress on propagation of unloaded indentation cracks in a PZT-5 ceramic has been studied. The results show that residual stress itself is too small to induce delayed propagation of the indentation cracks in silicon oil. If applied constant electric field is larger than 0.2 kV/cm, the combined effect of electric field and residual stress can cause delayed propagation of the indentation crack after passing an incubation time in silicon oil, but the crack will arrest after propagating for 10-30 μm because of decrease of the resultant stress intensity factor induced by the field and residual stress with increasing the crack length. The threshold electric field for delayed propagation of the indentation crack in silicon oil is E DP = 0.2 kV/cm. If the applied electric field is larger than 5.25 kV/cm, combined effect of the electric field and residual stress can cause instant propagation of the indentation crack, and under sustained electric field, the crack which has propagated instantly can propagate continuously, until arrest at last. The critical electric field for instant propagation of the indentation crack is E P = 5.25 kV/cm. If the applied electric field is larger than 12.6 kV/cm, the microcracks induced by the electric field initiate everywhere, grow and connect in a smooth specimen, resulting in delayed failure, even without residual stress. The threshold electric field for delayed failure of a smooth specimen in silicon oil is E DF = 12.6 kV/cm and the critical electric field for instant failure is E F = 19.1 kV/cm
Effect of temperature upon the fatigue-crack propagation behavior of Inconel 625
International Nuclear Information System (INIS)
James, L.A.
1977-03-01
The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of mill-annealed Inconel 625 in an air environment over the range 75 0 - 1200 0 F (24 0 - 649 0 C). In general, fatigue-crack growth rates increased with increasing test temperature. Two different specimen sizes were employed at each test temperature, and no effects of specimen size upon crack growth were noted
System for nucleation and propagation of fatigue cracks on SE(B) specimens
International Nuclear Information System (INIS)
Rocha, Nirlando Antonio; Gomes Junyor, Jose Onesimo; Reis, Emil; Vilela, Jefferson Jose; Moura, Cassio Melo
2015-01-01
The degree of safety that a structural component has against catastrophic fracture in service can be obtained from fracture mechanics parameters. The master curve could be used for integrity evaluation in pressure vessel of nuclear power plant. The pre-crack specimens are used in this evaluation. The tests based on ASTM E 8M and ASTM E 647 standards to determination of material properties related to fracture mechanics, most often performed in a servo-hydraulic drive equipment, are time consuming and costly. This paper presents the development of a system for nucleation and propagation of fatigue cracks on SE(B) specimens. The operating principle consists of a cyclic loading, concentrated in the center of the specimen, transmitted and controlled by an eccentric mechanism. The main contribution of this work is the low-cost technology in the production of fatigue pre-crack, and the possibility of performing the nucleation and propagation of the pre-crack required for obtaining the J IC and CTOD parameters. The experimental results satisfied expectations with respect to the plastic deformation in the crack tip and met the requirements of the standards. (author)
System for nucleation and propagation of fatigue cracks on SE(B) specimens
Energy Technology Data Exchange (ETDEWEB)
Rocha, Nirlando Antonio; Gomes Junyor, Jose Onesimo; Reis, Emil; Vilela, Jefferson Jose, E-mail: nar@cdtn.br, E-mail: ze_onezo@hotmail.com, E-mail: emilr@cdtn.br, E-mail: jjv@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil); Moura, Cassio Melo, E-mail: cassio.moura@gerdau.com.br [Gerdau S.A., Ouro Branco, MG (Brazil)
2015-07-01
The degree of safety that a structural component has against catastrophic fracture in service can be obtained from fracture mechanics parameters. The master curve could be used for integrity evaluation in pressure vessel of nuclear power plant. The pre-crack specimens are used in this evaluation. The tests based on ASTM E 8M and ASTM E 647 standards to determination of material properties related to fracture mechanics, most often performed in a servo-hydraulic drive equipment, are time consuming and costly. This paper presents the development of a system for nucleation and propagation of fatigue cracks on SE(B) specimens. The operating principle consists of a cyclic loading, concentrated in the center of the specimen, transmitted and controlled by an eccentric mechanism. The main contribution of this work is the low-cost technology in the production of fatigue pre-crack, and the possibility of performing the nucleation and propagation of the pre-crack required for obtaining the J{sub IC} and CTOD parameters. The experimental results satisfied expectations with respect to the plastic deformation in the crack tip and met the requirements of the standards. (author)
Effects of friction and high torque on fatigue crack propagation in mode III
International Nuclear Information System (INIS)
Nayeb-Hashemi, H.; McClintock, F.A.; Ritchie, R.O.
1982-01-01
Turbo-generator and automotive shafts are often subjected to complex histories of high torques. To provide a basis for fatigue life estimation in such components, a study of fatigue crack propagation in Mode III (anti-plane shear) for a mill-annealed AISI 4140 steel (R /SUB B/ 88, 590 MN/m 2 tensile strength) has been undertaken, using torsionally-loaded, circumferentially-notched cylindrical specimens. As demonstrated previously for higher strength AISI 4340 steel, Mode III cyclic crack growth rates (dc/dN) /SUB III/ can be related to the alternating stress intensity factor ΔK /SUB III/ for conditions of small-scale yielding. However, to describe crack propagation behavior over an extended range of crack growth rates (about 10 -6 to 10 -2 mm per cycle), where crack growth proceeds under elastic-plastic and full plastic conditions, no correlation between (dc/dN) /SUB III/ and ΔK /SUB III/ is possible. Accordingly, a new parameter for torsional crack growth, termed the plastic strain intensity GAMMA /SUB III/, is introduced and is shown to provide a unique description of Mode III crack growth behavior for a wide range of testing conditions, provided a mean load reduces friction, abrasion, and interlocking between mating fracture surfaces A micro-mechanical model for the main radial Mode III growth is extended to high nominal stress levels, and predicts that Mode III fatigue crack propagation rates should be proportional to the range of plastic strain intensity (ΔGAMMA /SUB III/) if local Mode II growth rates are proportional to the displacements. Such predictions are shown to be in agreement with measured growth rates in AISI 4140 steel from 10 -6 to 10 -2 mm per cycle
Compressive performance and crack propagation in Al alloy/Ti{sub 2}AlC composites
Energy Technology Data Exchange (ETDEWEB)
Hanaor, D.A.H., E-mail: dorian.hanaor@sydney.edu.au [School of Civil Engineering, University of Sydney, Sydney, NSW 2006 (Australia); Hu, L. [Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011 (United States); Kan, W.H.; Proust, G. [School of Civil Engineering, University of Sydney, Sydney, NSW 2006 (Australia); Foley, M. [Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, NSW 2006 (Australia); Karaman, I.; Radovic, M. [Department of Materials Science and Engineering, Texas A& M University, College Station, TX 77843 (United States)
2016-08-30
Composite materials comprising a porous Ti{sub 2}AlC matrix and Al 6061 alloy were fabricated by a current-activated pressure assisted melt infiltration process. Coarse, medium and fine meso-structures were prepared with Al alloy filled pores of differing sizes. Materials were subjected to uniaxial compressive loading up to stresses of 668 MPa, leading to the failure of specimens through crack propagation in both phases. As-fabricated and post-failure specimens were analysed by X-ray microscopy and electron microscopy. Quasi-static mechanical testing results revealed that compressive strength was the highest in the fine structured composite materials. While the coarse structured specimens exhibited a compressive strength of 80% relative to this. Reconstructed micro-scale X-ray tomography data revealed different crack propagation mechanisms. Large planar shear cracks propagated throughout the fine structured materials while the coarser specimens exhibited networks of branching cracks propagating preferentially along Al alloy-Ti{sub 2}AlC phase interfaces and through shrinkage pores in the Al alloy phase. Results suggest that control of porosity, compensation for Al alloy shrinkage and enhancement of the Al alloy-Ti{sub 2}AlC phase interfaces are key considerations in the design of high performance metal/Ti{sub 2}AlC phase composites.
International Nuclear Information System (INIS)
Boursier, Jean-Marie
1993-01-01
Stress corrosion cracking of Alloy 600 steam generator tubing is a great concern for pressurized water reactors. The mechanism that controls intergranular stress corrosion cracking of Alloy 600 in primary water (lithiated-borated water) has yet to be clearly identified. A study of stress corrosion cracking behaviour, which can identify the main parameters that control the cracking phenomenon, was so necessary to understand the stress corrosion cracking process. Constant extension rate tests, and constant load tests have evidenced that Alloy 600 stress corrosion cracking involves firstly an initiation period, then a slow propagation stage with crack less than 50 to 80 micrometers, and finally a rapid propagation stage leading to failure. The influence of mechanical parameters have shown the next points: - superficial strain hardening and cold work have a strong effect of stress corrosion cracking resistance (decrease of initiation time and increase of crack growth rate), - strain rate was the most suitable parameter for describing the different stage of propagation. The creep behaviour of alloy 600 has shown an increase of creep rate in primary water compared to air, which implies a local interaction plasticity/corrosion. An assessment of the durations of the initiation and the propagation stages was attempted for the whole uniaxial tensile tests, using the macroscopic strain rate: - the initiation time is less than 100 hours and seems to be an electrochemical process, - the durations of the propagation stage are strongly dependent on the strain rate. The behaviour in high primary water temperature of Alloys 690 and 800, which replace Alloy 600, was studied to appraise their margin, and validate their choice. Then the last chapter has to objective to evaluate the crack tip strain rate, in order to better describe the evolution of the different stages of cracking. (author) [fr
Analysis of parameters effects on crack breathing and propagation in shaft of rotor dynamic systems
Directory of Open Access Journals (Sweden)
M. Serier
2013-01-01
Full Text Available In this paper the design of experiment method is used to investigate and explain the effects of the rotor parameters on crack breathing and propagation in the shaft. Three factors are considered which have an influence on the behavior and the propagation of the crack: the rotational speed, the length of the rotor and the diameter of the shaft. The elaborated mathematical model allows determining the effects and interaction of speed, diameter and length on crack breathing mechanism.The model also determines the optimal values of the parameters to achieve high performance.
International Nuclear Information System (INIS)
Junru, Yang; Chuanjuan, Song; Minglan, Wang; Yeukan, Zhang; Jing, Sun
2016-01-01
The interface crack propagation problem in the cermet cladding material structure was studied. A comparative propagation property parameter (CP) suitable to judge the propagation direction of the interface crack in the cermet cladding material structure was proposed. The interface crack propagation criterion was established. Theoretical models of the CPs for the crack normal to and dwelling on the interface deflecting separately into the clad, the interface and the substrate were built, and the relations between the CPs and the load action angle, the clad thickness ratio and the load were investigated with an example. The research results show that, under the research conditions, the interface crack will more easily propagate into the clad layer than into the substrate
Energy Technology Data Exchange (ETDEWEB)
Junru, Yang; Chuanjuan, Song; Minglan, Wang; Yeukan, Zhang; Jing, Sun [College of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Qingdao (China)
2016-01-15
The interface crack propagation problem in the cermet cladding material structure was studied. A comparative propagation property parameter (CP) suitable to judge the propagation direction of the interface crack in the cermet cladding material structure was proposed. The interface crack propagation criterion was established. Theoretical models of the CPs for the crack normal to and dwelling on the interface deflecting separately into the clad, the interface and the substrate were built, and the relations between the CPs and the load action angle, the clad thickness ratio and the load were investigated with an example. The research results show that, under the research conditions, the interface crack will more easily propagate into the clad layer than into the substrate.
International Nuclear Information System (INIS)
Pelee-De-Saint-Maurice, Romains
2014-01-01
This PhD thesis presents numerical methods is dedicated to three-dimensional crack propagation in the framework of fast explicit structural dynamics using EUROPLEXUS software (currently abbreviated EPX, co-owned by CEA and EC/JRC). An approach based on the well-known XFEM method is proposed, representing the crack through level set functions. Special care is given to the update of the level set functions from the propagation velocity expressed on the crack edge, since the most widely used method based on the solution of Hamilton-Jacobi equations lacks robustness for fast transient crack propagations, even when level-sets are computed on an auxiliary regular finite difference grid. It is therefore chosen instead to implement a 3D approximated geometric method to update both level-sets. As far as failure mechanics is concerned, a local stress criterion on the edge of the crack, first developed by Haboussa et al., gives characteristic parameters of the material fracture. Mechanical equivalent quantities (strain, deformation) around the crack front are weighted by a Gaussian function, which gives more importance to Gauss integration points located near the crack tip. The maximum of the equivalent stress tensor near the crack tip gives the direction of the crack, and the Kanninen equation gives the crack velocity. Besides, because of the discontinuous displacement field, the numerical integration for elements cut by the crack yields performance issues. Increasing the number of quadrature points is CPU time consuming and quite hard to handle if it is chosen to change the number of points only for elements in the vicinity of the crack. Another approach tested here consists in keeping constant the number and position of quadrature points and modifying their weights in cut elements to obtain an accurate integration of several reference discontinuous fields. The proposed methods are tested and validated on significant examples, both two-dimensional, to ensure the backward
International Nuclear Information System (INIS)
Ferrie, Emilie; Buffiere, Jean-Yves; Ludwig, Wolfgang; Gravouil, Anthony; Edwards, Lyndon
2006-01-01
The propagation of a semi-elliptical crack in the bulk of an ultrafine-grained Al-Li alloy has been investigated using synchrotron radiation X-ray microtomography. In this material, the studied crack, despite its small dimension, can be considered as 'microstructurally long' and described in the frame of the linear elastic fracture mechanics. The extended finite element method is used to calculate the stress intensity factors along the crack front taking into account the three-dimensional geometry extracted from the tomographic images. For the same nominal value of the stress intensity factor range, crack propagation is faster in the bulk than at the surface. The observed anisotropy is attributed to the variation of the closure stress along the crack front between surface and bulk. The experimentally observed fatigue crack propagation is compared to numerical simulations. Good agreement is found when a linear variation of closure stress along the crack front is taken into account in the '3D crack propagation law' used for the simulation
International Nuclear Information System (INIS)
Wang Jianwei; Lu Guocai; Shang Xinchun
2011-01-01
The process of I-mode crack propagations in α-Fe for uniaxial tension experiments are simulated by molecular dynamics (MD) methods. The formation process of dislocation and fracture mechanisms in the crack growing under various temperatures were studied. The results show that the crack propagation is a process of successive emission of dislocation. The dislocation-free zone and the stacking faults were initially formed at crack tip. When the stress K I increased into 0. 566 MPam 1/2 , one layer of atoms near crack tip would be separated into two layers which produced a dislocation. The first dislocation was emitted when stress K I reached 0.669 MPam 1/2 . With the temperature increasing, the critical stress intensity factor decreased gradually and the dislocation emission correspondingly became faster as well. (authors)
Energy Technology Data Exchange (ETDEWEB)
Menouillard, T
2007-09-15
Computerized simulation is nowadays an integrating part of design and validation processes of mechanical structures. Simulation tools are more and more performing allowing a very acute description of the phenomena. Moreover, these tools are not limited to linear mechanics but are developed to describe more difficult behaviours as for instance structures damage which interests the safety domain. A dynamic or static load can thus lead to a damage, a crack and then a rupture of the structure. The fast dynamics allows to simulate 'fast' phenomena such as explosions, shocks and impacts on structure. The application domain is various. It concerns for instance the study of the lifetime and the accidents scenario of the nuclear reactor vessel. It is then very interesting, for fast dynamics codes, to be able to anticipate in a robust and stable way such phenomena: the assessment of damage in the structure and the simulation of crack propagation form an essential stake. The extended finite element method has the advantage to break away from mesh generation and from fields projection during the crack propagation. Effectively, crack is described kinematically by an appropriate strategy of enrichment of supplementary freedom degrees. Difficulties connecting the spatial discretization of this method with the temporal discretization of an explicit calculation scheme has then been revealed; these difficulties are the diagonal writing of the mass matrix and the associated stability time step. Here are presented two methods of mass matrix diagonalization based on the kinetic energy conservation, and studies of critical time steps for various enriched finite elements. The interest revealed here is that the time step is not more penalizing than those of the standard finite elements problem. Comparisons with numerical simulations on another code allow to validate the theoretical works. A crack propagation test in mixed mode has been exploited in order to verify the simulation
Fatigue crack propagation and delamination growth in Glare
Alderliesten, R.C.
2005-01-01
Fibre Metal Laminate Glare consists of thin aluminium layers bonded together with pre-impregnated glass fibre layers and shows an excellent fatigue crack growth behaviour compared to monolithic aluminium. The fibres are insensitive to the occurring fatigue loads and remain intact while the fatigue
On the transition of short cracks into long fatigue cracks in reactor pressure vessel steels
Directory of Open Access Journals (Sweden)
Singh Rajwinder
2018-01-01
Full Text Available Short fatigue cracks, having dimension less than 1 mm, propagate at much faster rates (da/dN even at lower stress intensity factor range (da/dN as compared to the threshold stress intensity factor range obtained from long fatigue crack growth studies. These short cracks originate at the sub-grain level and some of them ultimately transit into critical long cracks over time. Therefore, designing the components subjected to fatigue loading merely on the long crack growth data and neglecting the short crack growth behavior can overestimate the component’s life. This aspect of short fatigue cracks become even more critical for materials used for safety critical applications such as reactor pressure vessel (RPV steel in nuclear plants. In this work, the transition behaviour of short fatigue crack gowth into long fatigue crack is studied in SA508 Grade 3 Class I low alloy steel used in RPVs. In-situ characterization of initiation, propagation and transition of short fatigue cracks is performed using fatigue stage for Scanning Electron Microscope (SEM in addition to digital microscopes fitted over a servo-hydraulic fatigue machine and correlated with the microtructural information obtained using electron backscatter diffraction (EBSD. SA508 steel having an upper bainitic microstructure have several microstructural interfaces such as phase and grain boundaries that play a significant role in controlling the short fatigue crack propagation. Specially designed and prepared short fatigue specimens (eletro-polished with varying initial crack lengths of the order of tens of microns are used in this study. The transition of such short initial cracks into long cracks is then tracked to give detailed insight into the role of each phase and phase/grain boundary with an objective of establishing Kitagawa-Takahashi diagram for the given RPV steel. The behavior of the transited long cracks is then compared with the crack propagation behavior obtained using
International Nuclear Information System (INIS)
Van Brutzel, L.
2000-01-01
The aim of this thesis was to understand the mechanism which occurs during the crack at the atomic scale in amorphous silica. The difficulties of the experimental observations at this length scale lead us to use numerical studies by molecular dynamics to access to the dynamical and the thermodynamical informations. We have carried out large simulations with 500000 atoms and studied the structure of the amorphous silica before to studying their behaviours under an imposed strain. The structure of this simulated amorphous silica settled in three length scales. In small length scale between 0 and 5 angstrom glass is composed of tetrahedra, this is close to the crystalline structure. In intermediate length scale between 3 and 10 angstrom tetrahedra are connected together and build rings of different sizes composed in majority between 5 and 7 tetrahedra. In bigger length scale between 15 and 60 angstrom, areas with high density of rings are surrounded by areas with low density of rings. These structural considerations play an important role in initiation and propagation of a crack. Indeed. in this length scale. crack propagates by growth and coalescence of some small cavities which appear in area with low density of rings behind the crack tip. The cavities dissipate the stress with carries away a delay to propagation of the crack. This phenomenons seems ductile and leads to non linear elastic behaviour near the crack tip. We have also shown that the addition of alkali in the amorphous silica changes the structure by creation of nano-porosities and leads to enhance the ductility during the crack propagation. (author)
Criterion of cleavage crack propagation and arrest in a nuclear PWR vessel steel
International Nuclear Information System (INIS)
Bousquet, Amaury
2013-01-01
The purpose of this PhD thesis is to understand physical mechanisms of cleavage crack propagation and arrest in the 16MND5 PWR vessel steel and to propose a robust predicting model based on a brittle fracture experimental campaign of finely instrumented laboratory specimens associated with numerical computations. First, experiments were carried out on thin CT25 specimens at five temperatures (-150 C, -125 C, -100 C, -7 C, -50 C). Two kinds of crack path, straight or branching path, have been observed. To characterize crack propagation and to measure crack speed, a high-speed framing camera system was used, combined with the development of an experimental protocol which allowed to observe CT surface without icing inside the thermal chamber and on the specimen. The framing camera (520 000 fps) has allowed to have a very accurate estimation of crack speed on the complete ligament of CT (∼ 25 mm). Besides, to analyse experiments and to study the impact of viscosity on the mechanical response around the crack tip, the elastic-viscoplastic behavior of the ferritic steel has been studied up to a strain rate of 104 s -1 for the tested temperatures.The extended Finite Element Method (X-FEM) was used in CAST3M FE software to model crack propagation. Numerical computations combine a local non linear dynamic approach with a RKR type fracture stress criterion to a characteristic distance. The work carried out has confirmed the form of the criterion proposed by Prabel at -125 C, and has identified the dependencies of the criterion on temperature and strain rate. From numerical analyzes in 2D and 3D, a multi-temperature fracture stress criterion, increasing function of the strain rate, was proposed. Predictive modeling were used to confirm the identified criterion on two specimen geometries (CT and compressive ring) in mode I at different temperatures. SEM observations and 3D analyzes made with optical microscope showed that the fracture mechanism was the cleavage associated
G-control fatigue testing for cyclic crack propagation in composite structures
DEFF Research Database (Denmark)
Manca, Marcello; Berggreen, Christian; Carlsson, Leif A.
2015-01-01
This paper presents a computer controlled testing methodology called “The G-control Method” which allows cyclic crack growth testing using real-time control of the cyclic energy release rate. The advantages of using this approach are described and compared with traditional fatigue testing methods...... that the G-control method allows fatigue testing at a constant range of energy release rates leading to a constant crack propagation rate....
Rudraraju, Siva Shankar; Garikipati, Krishna; Waas, Anthony M.; Bednarcyk, Brett A.
2013-01-01
The phenomenon of crack propagation is among the predominant modes of failure in many natural and engineering structures, often leading to severe loss of structural integrity and catastrophic failure. Thus, the ability to understand and a priori simulate the evolution of this failure mode has been one of the cornerstones of applied mechanics and structural engineering and is broadly referred to as "fracture mechanics." The work reported herein focuses on extending this understanding, in the context of through-thickness crack propagation in cohesive materials, through the development of a continuum-level multiscale numerical framework, which represents cracks as displacement discontinuities across a surface of zero measure. This report presents the relevant theory, mathematical framework, numerical modeling, and experimental investigations of through-thickness crack propagation in fiber-reinforced composites using the Variational Multiscale Cohesive Method (VMCM) developed by the authors.
Low temperature spalling of silicon: A crack propagation study
Energy Technology Data Exchange (ETDEWEB)
Bertoni, Mariana; Uberg Naerland, Tine; Stoddard, Nathan; Guimera Coll, Pablo
2017-06-08
Spalling is a promising kerfless method for cutting thin silicon wafers while doubling the yield of a silicon ingot. The main obstacle in this technology is the high total thickness variation of the spalled wafers, often as high as 100% of the wafer thickness. It has been suggested before that a strong correlation exists between low crack velocities and a smooth surface, but this correlation has never been shown during a spalling process in silicon. The reason lies in the challenge associated to measuring such velocities. In this contribution, we present a new approach to assess, in real time, the crack velocity as it propagates during a low temperature spalling process. Understanding the relationship between crack velocity and surface roughness during spalling can pave the way to attain full control on the surface quality of the spalled wafer.
International Nuclear Information System (INIS)
Chen Zhitong; Li Guang; Wu Zhenqiang; Xia Yuan
2011-01-01
Research highlights: → Composite coatings on the aluminized steel were prepared by the plasma electrolytic oxidation (PEO) technique, which comprised of Fe-Al layer, Al layer and Al 2 O 3 layer. → The evaluation method of the crack critical opening displacement δ c was introduced to describe quantitatively the resistance of Al layer to the propagation behavior of cracks and evaluate the fracture behavior of composite coatings. → The crack propagating model was established. - Abstract: This paper investigates the in situ tensile cracks propagating behavior of composite coatings on the aluminized steel generated using the plasma electrolytic oxidation (PEO) technique. Cross-sectional micrographs and elemental compositions were investigated by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The composite coatings were shown to consist of Fe-Al, Al and Al 2 O 3 layers. The cracks propagating behavior was observed in real-time in situ SEM tensile test. In tensile process, the cracks were temporarily stopped when cracks propagated from Fe-Al layer to Al layer. The critical crack opening displacement δ c was introduced to quantitatively describe the resistance of the Al layer. There was a functional relation among the thickness ratio t Al /t Al 2 O 3 , the δ c of composite coatings and tensile cracks' spacing. The δ c increased with the increasing of the thickness ratio (t Al /t Al 2 O 3 ). The high δ c value means high fracture resistance. Therefore, a control of the thickness ratio t Al /t Al 2 O 3 was concerned as a key to improve the toughness and strength of the aluminized steel.
Investigations on creep and creep fatigue crack behaviour for component assessment
International Nuclear Information System (INIS)
Gengenbach, T.; Klenk, A.; Maile, K.
2004-01-01
There are various methods to assess crack initiation and crack growth behaviour of components under creep and creep fatigue loading. The programme system HT-Riss has been developed to support calculations aimed to determine the behaviour of a crack under creep or creep-fatigue loading using methods based on stress-intensity factor K (e.g. the Two-Criteria-Diagram) or C*-Integral. This paper describes the steps which have to be performed to assess crack initiation and growth of a component using this programme system. First the size of the maximum initial defect in a specimen or in a component has to be estimated and the necessary fracture mechanics parameters have to be determined. Then the time for creep crack initiation and creep crack growth is calculated. Using these values a prediction of life time and necessary inspection intervals is possible. For exemplification the crack assessment of a component-like specimen and a component is shown. (orig.)
Fatigue behaviour and crack growth of ferritic steel under environmental conditions
International Nuclear Information System (INIS)
Herter, K.H.; Schuler, X.; Weissenberg, T.
2012-01-01
The assessment of fatigue and cyclic crack growth behaviour of safety relevant components is of importance for the ageing management with regard to safety and reliability. For cyclic stress evaluation different codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as a limiting criteria the influence of different factors like e.g. environment, surface finish and temperature must be taken into consideration in an appropriate way. Fatigue tests were performed in the low cycle fatigue (LCF) und high cycle fatigue (HCF) regime with low alloy steels as well as with Nb- and Ti-stabilized German austenitic stainless steels in air and high temperature (HT) boiling water reactor environment to extend the state of knowledge of environmentally assisted fatigue (EAF) as it can occur in boiling water reactor (BWR) plants. Using the reactor pressure vessel (RPV) steel 22NiMoCr3-7 experimental data were developed to verify the influence of BWR coolant environment (high purity water as well as sulphate containing water with 90 ppb SO 4 at a test temperature of 240 C and an oxygen content of 400 ppb) on the fatigue life and to extend the basis for a reliable estimation of the remaining service life of reactor components. Corresponding experiments in air were performed to establish reference data to determine the environmental correction factor F en accounting for the environment. The experimental results are compared with international available mean data curves, the new design curves and on the basis of the environmental factor F en . Furthermore the behaviour of steel 22NiMoCr3-7 in oxygenated high temperature water under transient loading conditions was investigated with respect to crack initiation and cyclic crack growth. In this process the stress state of the specimen and the chemical composition of the high
Effect of temperature upon the fatigue-crack propagation behavior of Inconel X-750
International Nuclear Information System (INIS)
James, L.A.
1976-05-01
The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of precipitation heat-treated Inconel X-750 in an air environment over the range 75-1200 0 F. In general, fatigue-crack growth rates increased with increasing test temperature
Numerical modelling of desiccation cracking of clayey soil
Directory of Open Access Journals (Sweden)
Vo Thi Dong
2016-01-01
Full Text Available The formation and propagation of desiccation cracks in soil is an extremely complex phenomenon because of the coupling between hydraulic and mechanical behaviour of soil, which are constituted here by the presence of capillary forces and discontinuities. The formation of a cracks network strongly influences the mechanical and hydraulic properties of soil. The main objective of this research is to study the evolution of suction and strain fields, the initiation and propagation of cracks under the effect of drying, using the finite element method. A simulation of a soil sample with four cohesive joints shows the results similar to experimental data. In addition, a simulation of multijoints shows that cracks does not open in all potentials positions and it gives similar spacing.
Comparative Study on Crack Initiation and Propagation of Glass under Thermal Loading
Directory of Open Access Journals (Sweden)
Yu Wang
2016-09-01
Full Text Available This paper explores the fracture process based on finite element simulation. Both probabilistic and deterministic methods are employed to model crack initiation, and several commonly used criteria are utilized to predict crack growth. It is concluded that the criteria of maximum tensile stress, maximum normal stress, and maximum Mises stress, as well as the Coulomb-Mohr criterion are able to predict the initiation of the first crack. The mixed-mode criteria based on the stress intensity factor (SIF, energy release rate, and the maximum principal stress, as well as the SIF-based maximum circumferential stress criterion are suitable to predict the crack propagation.
A method for the 3-D quantification of bridging ligaments during crack propagation
International Nuclear Information System (INIS)
Babout, L.; Janaszewski, M.; Marrow, T.J.; Withers, P.J.
2011-01-01
This letter shows how a hole-closing algorithm can be used to identify and quantify crack-bridging ligaments from a sequence of X-ray tomography images of intergranular stress corrosion cracking. This allows automatic quantification of the evolution of bridging ligaments through the crack propagation sequence providing fracture mechanics insight previously unobtainable from fractography. The method may also be applied to other three-dimensional materials science problems, such as closing walls in foams.
Cai, Yecheng; Wang, Maolu; Zhang, Hongzhi; Yang, Lijun; Fu, Xihong; Wang, Yang
2017-08-01
Silicon-glass devices are widely used in IC industry, MEMS and solar energy system because of their reliability and simplicity of the manufacturing process. With the trend toward the wafer level chip scale package (WLCSP) technology, the suitable dicing method of silicon-glass bonded structure wafer has become necessary. In this paper, a combined experimental and computational approach is undertaken to investigate the feasibility of cutting the sandwich structure glass-silicon-glass (SGS) wafer with laser induced thermal-crack propagation (LITP) method. A 1064 nm semiconductor laser cutting system with double laser beams which could simultaneously irradiate on the top and bottom of the sandwich structure wafer has been designed. A mathematical model for describing the physical process of the interaction between laser and SGS wafer, which consists of two surface heating sources and two volumetric heating sources, has been established. The temperature stress distribution are simulated by using finite element method (FEM) analysis software ABAQUS. The crack propagation process is analyzed by using the J-integral method. In the FEM model, a stationary planar crack is embedded in the wafer and the J-integral values around the crack front edge are determined using the FEM. A verification experiment under typical parameters is conducted and the crack propagation profile on the fracture surface is examined by the optical microscope and explained from the stress distribution and J-integral value.
Crack propagation direction in a mixed mode geometry estimated via multi-parameter fracture criteria
Czech Academy of Sciences Publication Activity Database
Malíková, L.; Veselý, V.; Seitl, Stanislav
2016-01-01
Roč. 89, AUG (2016), s. 99-107 ISSN 0142-1123. [International Conference on Characterisation of Crack Tip Fields /3./. Urbino, 20.04.2015-22.04.2015] Institutional support: RVO:68081723 Keywords : Near-crack-tip fields * Mixed mode * Crack propagation direction * Multi-parameter fracture criteria * Finite element analysis Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.899, year: 2016
Finite element analysis of crack growth from rectangular notch in mixed mode loading
International Nuclear Information System (INIS)
Mohd Rawi Mohd Zin
2002-01-01
The direction of crack growth from rectangular notch for ductile material is determined in this paper. The ductile material is assumed to exhibit the elastic-plastic behaviour. In the model, the crack is assumed to start when the J-integral fracture criterion exceeded the critical value during the application of load and the crack tip propagated to a priori. The direction of the crack is characterised by maximum principles stress criterion and the mechanism of crack propagation is simulated by deleted element technique. The model is validated with experimental results and it shows good agreement. (Author)
Effects of Changing Stress Amplitude on the Rate of Fatigue-Crack Propagation in Two Aluminum Alloys
Hudson, C. Michael; Hardrath, Herbert F.
1961-01-01
A series of fatigue tests with specimens subjected to constant amplitude and two-step axial loads were conducted on 12-inch-wide sheet specimens of 2024-T3 and 7075-T6 aluminum alloy to study the effects of a change in stress level on fatigue-crack propagation. Comparison of the results of the tests in which the specimens were tested at first a high and then a low stress level with those of the constant-stress- amplitude tests indicated that crack propagation was generally delayed after the transition to the lower stress level. In the tests in which the specimens were tested at first a low and then a high stress level, crack propagation continued at the expected rate after the change in stress levels.
Crack propagation rate modelling for 316SS exposed to PWR-relevant conditions
International Nuclear Information System (INIS)
Vankeerberghen, M.; Weyns, G.; Gavrilov, S.; Martens, B.; Deconinck, J.
2009-01-01
The crack propagation rate of Type 316 stainless steel in boric acid-lithium hydroxide solutions under PWR-relevant conditions was modelled. A film rupture/dissolution/repassivation mechanism is assumed and extended to cold worked materials by including a stress-dependent bare metal dissolution current density. The chemical and electrochemical conditions within the crack are calculated by finite element calculations, an analytical expression is used for the crack-tip strain rate and the crack-tip stress is assumed equal to 2.5 times the yield stress (plane-strain). First the model was calibrated against a literature published data set. Afterwards, the influence of various variables - dissolved hydrogen, boric acid and lithium hydroxide content, stress intensity, crack length, temperature, flow rate - was studied. Finally, other published crack growth rate tests were modelled and the calculated crack growth rates were found to be in reasonable agreement with the reported ones
Energy Technology Data Exchange (ETDEWEB)
Chongchong, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Lihong, Dong, E-mail: lihong.dong@126.com [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Haidou, Wang [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Guolu, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Binshi, Xu [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China)
2016-05-01
Monitoring fatigue crack propagation behavior of ferromagnetic components is very important. In this paper, the tension–tension fatigue tests of center cracked tension (CCT) specimens were carried out; the variation regularity of both tangential and normal components of magnetic signals during fatigue process were investigated. The results showed that the initial abnormal signals which appeared at the notch were reversed after cyclic loading. The abnormal magnetic signals became more significant with the increase of fatigue cycles and reversed again after failure. The characteristic parameters, i.e., the peak value of tangential component, B{sub tp}, and maximum gradient value of normal component, K{sub m}, showed similar variation trends during the fatigue process, which can be divided into three different stages. An approximate linear relationship was found between the characteristic parameters and fatigue crack length 2a. The feasibility of predicting the fatigue crack propagation using the abnormal magnetic signals was discussed. What's more, the variation and distribution of the magnetic signals were also analyzed based on the theory of magnetic charge. - Highlights: • A novel and passive NDT method, i.e. MMMT method, is proposed. • Both tangential and normal components of magnetic signals were investigated. • The prediction of crack propagation by abnormal magnetic signals was discussed. • A linear relationship was found between the parameters and fatigue crack length 2a. • The parameters can be potentially used to evaluate the crack propagation state.
Simulation of crack propagation in rock in plasma blasting technology
Ikkurthi, V. R.; Tahiliani, K.; Chaturvedi, S.
Plasma Blasting Technology (PBT) involves the production of a pulsed electrical discharge by inserting a blasting probe in a water-filled cavity drilled in a rock, which produces shocks or pressure waves in the water. These pulses then propagate into the rock, leading to fracture. In this paper, we present the results of two-dimensional hydrodynamic simulations using the SHALE code to study crack propagation in rock. Three separate issues have been examined. Firstly, assuming that a constant pressure P is maintained in the cavity for a time τ , we have determined the P- τ curve that just cracks a given rock into at least two large-sized parts. This study shows that there exists an optimal pressure level for cracking a given rock-type and geometry. Secondly, we have varied the volume of water in which the initial energy E is deposited, which corresponds to different initial peak pressures Ppeak. We have determined the E- Ppeak curve that just breaks the rock into four large-sized parts. It is found that there must be an optimal Ppeak that lowers the energy consumption, but with acceptable probe damage. Thirdly, we have attempted to identify the dominant mechanism of rock fracture. We also highlight some numerical errors that must be kept in mind in such simulations.
Experimental investigation into the crack propagation in multiphase tantalum carbide ceramics
Energy Technology Data Exchange (ETDEWEB)
Schulz, Bradford C. [Department of Metallurgical & Materials Engineering, The University of Alabama, 301 7th Avenue, 116 Houser Hall, Tuscaloosa, AL 35487-0202 (United States); Lee, HeeDong; Mogilevsky, Pavel [UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432-1894 (United States); Weinberger, Christopher R. [Department of Mechanical Engineering, Colorado State University, 1374 Campus Delivery, Fort Collins, CO 80523 (United States); Parthasarathy, Triplicane A. [UES, Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432-1894 (United States); Matson, Lawrence E. [Air Force Research Laboratory Materials & Manufacturing Directorate, Structural Material Division (AFRL/RXLN), 2230 Tenth St., Wright-Patterson AFB, OH 4543307817 (United States); Smith, Chase [Department of Metallurgical & Materials Engineering, The University of Alabama, 301 7th Avenue, 116 Houser Hall, Tuscaloosa, AL 35487-0202 (United States); Thompson, Gregory B., E-mail: gthompson@eng.ua.edu [Department of Metallurgical & Materials Engineering, The University of Alabama, 301 7th Avenue, 116 Houser Hall, Tuscaloosa, AL 35487-0202 (United States)
2017-05-17
Tantalum carbide ceramics with high volume fractions of the ζ-Ta{sub 4}C{sub 3} phase have been shown to exhibit high fracture strength and toughness as compared to those in absence of this phase. In this work, we investigated how microcracks propagated in this these high toughness ceramics using Knoop and Vickers microindentation. The Knoop indentations demonstrated that cracking preferentially occurred parallel to the lath structure in ζ-Ta{sub 4}C{sub 3}; however shorter cracks did form between the laths when a sufficient driving force was present. The resulting crack path was tortuous providing direct evidence for toughening through crack deflection; however, the microscale nature of the work cannot rule out crack bridging as a toughening mechanism as well. Plasticity is also observed under the indents, but is likely a result of the high confining pressures that occurred during indentation allowing for plastic flow.
Investigations of subcritical crack propagation of the Empress 2 all-ceramic system.
Mitov, Gergo; Lohbauer, Ulrich; Rabbo, Mohammad Abed; Petschelt, Anselm; Pospiech, Peter
2008-02-01
The mechanical properties and slow crack propapagation of the all-porcelain system Empress 2 (Ivoclar Vivadent, Schaan, Liechtenstein) with its framework compound Empress 2 and the veneering compounds "Empress 2 and Eris were examined. For all materials, the fracture strength, Weibull parameter and elastic moduli were experimentally determined in a four-point-bending test. For the components of the Empress 2 system, the fracture toughness K(IC) was determined, and the crack propagation parameters n and A were determined in a dynamic fatigue method. Using these data, life data analysis was performed and lifetime diagrams were produced. The development of strength under static fatigue conditions was calculated for a period of 5 years. The newly developed veneering ceramic Eris showed a higher fracture strength (sigma(0)=66.1 MPa) at a failure probability of P(F)=63.2%, and crack growth parameters (n=12.9) compared to the veneering ceramic Empress 2 (sigma(0)=60.3 MPa). For Empress 2 veneer the crack propagation parameter n could only be estimated (n=9.5). This is reflected in the prognosis of long-term resistance presented in the SPT diagrams. For all materials investigated, the Weibull parameter m values (Empress 2 framework m=4.6; Empress 2 veneer m=7.9; Eris m=6.9) were much lower than the minimum demanded by the literature (m=15). The initial fracture strength value alone is not sufficient to characterize the mechanical resistance of ceramic materials, since their stressability is time-dependent. Knowledge about the crack propagation parameters n and A are of great importance when preclinically predicting the clinical suitability of dental ceramic materials. The use of SPT diagrams for lifetime calculation of ceramic materials is a valuable method for comparing different ceramics.
International Nuclear Information System (INIS)
Emery, A.F.; Kobayashi, A.S.; Love, W.J.
1978-04-01
This report contains the description of predictive models for the initiation and propagation of cracks in pipes and the numerical results obtained. The initiation of the crack was studied by evaluating stress intensity factors under static conditions for a series of representative flaws. Three-dimensional static stress intensity factors were determined for quarter-elliptical cracks at the corner of a hole in an infinite plate and at the corner of a bore in a rotating disk. Semi-elliptical cracks for plates in bending and in pressurized and thermally stressed hollow cylinders were also evaluated. The stress fields, in the absence of a crack, were used in the ''alternating technique'' to compute the stress intensity factors along the crack front. Parametric studies were made to assess the effects of crack thickness, the ratio of the major and minor axes of the ellipse and the thickness of the cylinders or plates. These parametric results may be used to predict critical flaw sizes for the initiation of the running crack. The initiation and propagation of axial through cracks in pressurized pipes was studied by using an elastic-plastic finite different shell code coupled with a one-dimensional thermal-hydraulic code which computed the leakage through the crack opening and the depressurization of the fluid in the pipe. The effects of large deflections and different fluid pressure profiles were investigated. The results showed that the crack opening shape is dependent upon the fracture criterion used and upon the average pressure on the crack flaps, but not upon the specific pressure profile. The consideration of large deflections changed the opening size of the crack and through the coupling with the pipe pressures, strongly affected the crack tip speed. However, for equal crack lengths, there was little difference between calculations made for large and small deflection
Luiz Carlos H. Ricardo; Carlos Alexandre J. Miranda
2016-01-01
Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique as criterion design. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading fr...
Pindra, Nadjime; Lazarus, Véronique; Leblond, Jean-Baptiste
One studies the evolution in time of the deformation of the front of a semi-infinite 3D interface crack propagating quasistatically in an infinite heterogeneous elastic body. The fracture properties are assumed to be lower on the interface than in the materials so that crack propagation is channelled along the interface, and to vary randomly within the crack plane. The work is based on earlier formulae which provide the first-order change of the stress intensity factors along the front of a semi-infinite interface crack arising from some small but otherwise arbitrary in-plane perturbation of this front. The main object of study is the long-time behavior of various statistical measures of the deformation of the crack front. Special attention is paid to the influences of the mismatch of elastic properties, the type of propagation law (fatigue or brittle fracture) and the stable or unstable character of 2D crack propagation (depending on the loading) upon the development of this deformation.
Effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280
International Nuclear Information System (INIS)
James, L.A.
1976-05-01
The techniques of linear-elastic fracture mechanics were employed to characterize the effect of temperature upon the fatigue-crack propagation behavior of Hastelloy X-280 in an air environment. Also included in this study are survey tests to determine the effects of thermal aging and stress ratio upon crack growth behavior in this alloy
International Nuclear Information System (INIS)
Brunner, A.; Nordstrom, R.; Flueeler, P.
1992-01-01
The described investigation of crack formation and crack propagation in mode I (tensile stress) in fibre-reinforced plastic samples, especially uni-directional carbon fibre reinforced polyether-ether ketone (PEEK) has several aims. On the one hand, the phenomena of crack formation and crack propagation in these materials are to be studied, and on the other hand, the draft standards for these tests are to be checked. It was found that the combination of real time X-ray tests and simultaneous sound emission analysis is excellently suited for the basic examination of crack formation and crack propagation in DCB samples. With the aid of picture processing and analysis of the video representation, consistent crack lengths and resulting G IC values can be determined. (orig./RHM) [de
International Nuclear Information System (INIS)
James, L.A.
1996-01-01
The effect of elevated temperature aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels is discussed in terms of the several parameters which influence such behavior. These parameters include water chemistry, impurities within the steels themselves, as well as factors such as the water flow rate, loading waveform and loading rates. Some of these parameters have similar effects upon both crack initiation and propagation, while others exhibit different effects in the two stages of cracking. In the case of environmentally-assisted crack (EAC) growth, the most important impurities within the steel are metallurgical sulfide inclusions which dissolve upon contact with the water. A ''critical'' concentration of sulfide ions at the crack tip can then induce environmentally-assisted cracking which proceeds at significantly increased crack growth rates over those observed in air. The occurrence, or non-occurrence, of EAC is governed by the mass-transport of sulfide ions to and from the crack-tip region, and the mass-transport is discussed in terms of diffusion, ion migration, and convection induced within the crack enclave. Examples are given of convective mass-transport within the crack enclave resulting from external free stream flow. The initiation of fatigue cracks in elevated temperature aqueous environments, as measured by the S-N fatigue lifetimes, is also strongly influenced by the parameters identified above. The influence of sulfide inclusions does not appear to be as strong on the crack initiation process as it is on crack propagation. The oxygen content of the environment appears to be the dominant factor, although loading frequency (strain rate) and temperature are also important factors
Effect of defect length on rolling contact fatigue crack propagation in high strength steel
Directory of Open Access Journals (Sweden)
T. Makino
2015-10-01
Full Text Available The objective of the present paper is to clarify the effect of defect length in depth direction on rolling contact fatigue (RCF crack propagation in high strength steel. RCF test and synchrotron radiation micro computed tomography (SR micro CT imaging were conducted. In the case of the defect with the 15 m diameter, flaking life decreased with increasing defect length. In a comparison of the CT image and the SEM view, the shapes of defects and the locations of the horizontal cracks were almost the same respectively. The mechanism of RCF crack propagation was discussed by finite element (FE analysis. Defects led to higher tensile residual stress than that without defects in the region where the defect exists. The shear stress range at 0.1 mm in depth on the middle line of the defect and the range of mode II stress intensity factor at the bottom of a vertical crack increased with increasing defect length.
Energy Technology Data Exchange (ETDEWEB)
Tomkins, B.
1975-05-01
The value of modelling the fatigue crack propagation process is discussed and current models are examined in the light of increasing knowledge of crack tip deformation. Elevated temperature fatigue is examined in detail as an area in which models could contribute significantly to engineering design. A model is developed which examines the role of time-dependent creep cavitation on the failure process in an interactive creep-fatigue situation. (auth)
Simulation of crack propagation in fiber-reinforced concrete by fracture mechanics
International Nuclear Information System (INIS)
Zhang Jun; Li, Victor C.
2004-01-01
Mode I crack propagation in fiber-reinforced concrete (FRC) is simulated by a fracture mechanics approach. A superposition method is applied to calculate the crack tip stress intensity factor. The model relies on the fracture toughness of hardened cement paste (K IC ) and the crack bridging law, so-called stress-crack width (σ-δ) relationship of the material, as the fundamental material parameters for model input. As two examples, experimental data from steel FRC beams under three-point bending load are analyzed with the present fracture mechanics model. A good agreement has been found between model predictions and experimental results in terms of flexural stress-crack mouth opening displacement (CMOD) diagrams. These analyses and comparisons confirm that the structural performance of concrete and FRC elements, such as beams in bending, can be predicted by the simple fracture mechanics model as long as the related material properties, K IC and (σ-δ) relationship, are known
Mode I Cohesive Law Characterization of Through-Crack Propagation in a Multidirectional Laminate
Bergan, Andrew C.; Davila, Carlos G.; Leone, Frank A.; Awerbuch, Jonathan; Tan, Tein-Min
2014-01-01
A method is proposed and assessed for the experimental characterization of through-the-thickness crack propagation in multidirectional composite laminates with a cohesive law. The fracture toughness and crack opening displacement are measured and used to determine a cohesive law. Two methods of computing fracture toughness are assessed and compared. While previously proposed cohesive characterizations based on the R-curve exhibit size effects, the proposed approach results in a cohesive law that is a material property. The compact tension specimen configuration is used to propagate damage while load and full-field displacements are recorded. These measurements are used to compute the fracture toughness and crack opening displacement from which the cohesive law is characterized. The experimental results show that a steady-state fracture toughness is not reached. However, the proposed method extrapolates to steady-state and is demonstrated capable of predicting the structural behavior of geometrically-scaled specimens.
Fatique crack propagation in bimetallic welds influence of residual stresses and metallurgical look
International Nuclear Information System (INIS)
Zahouane, A.I.
1988-06-01
Generally, in nuclear power plants, many components made of austenitic stainless steels are very often replaced by low alloyed steels cladded with stainless steels, mainly for economical reasons. Due to cracks existing at the limit of the two kinds of steel, it is interesting to try to understand how they appear. Residual stresses are generally identified as one of the factors which act to produce these cracks. Measurements of such residual stresses have been performed, using the hole drilling method (drilling of a hole at the center of a gauge roset stuck at the surface of the material). Owing to the obtained results, it is possible to explain the decrease in the crack propagation rate observed, on fatigue crack growth test performed on specimens taken in the transition ferritic/austenitic zone. The stress intensity factor due to the residual stresses is valued by weight function method. It is possible to explain qualitatively the phenomena observed under cyclic loading when using the obtained value of this stress intensity factor. A more quantitative approach based on the use of an efficient stress intensity factor, allow to better describe the effect of residual stresses on the fatigue crack propagation in bimetallic welds [fr
Crack propagation in stainless steel AISI 304L in Hydrogen Chemistry conditions (HWC)
International Nuclear Information System (INIS)
Diaz S, A.; Fuentes C, P.; Merino C, F.; Castano M, V.
2006-01-01
Velocities of crack growth in samples type CT pre cracking of stainless steel AISI 304l solder and sensitized thermally its were obtained by the Rising Displacement method or of growing displacement. It was used a recirculation circuit that simulates the operation conditions of a BWR type reactor (temperature of 280 C and a pressure of 8 MPa) with the chemistry modified by the addition of hydrogen with and without the addition of impurities of a powerful oxidizer like the Cu + ion. In each essay stayed a displacement velocity was constant of 1x10 -9 m/s, making a continuous pursuit of the advance of the crack by the electric potential drop technique. Contrary to the idea of mitigation of the crack propagation velocity by effect of the addition of the hydrogen in the system, the values of the growth velocities obtained by this methodology went similar to the opposing ones under normal operation conditions. To the finish of the rehearsal one carries out the fractographic analysis of the propagation surfaces, which showed cracks growth in trans and intergranular way, evidencing the complexity of the regulator mechanisms of the IGSCC like in mitigation conditions as the alternative Hydrogen Chemistry. (Author)
Directory of Open Access Journals (Sweden)
Dongyang Li
2017-01-01
Full Text Available Numerical and experimental methods were applied to investigate fatigue crack propagation behavior of reinforced concrete (RC beams strengthened with a new type carbon fiber reinforced polymer (CFRP named as carbon fiber laminate (CFL subjected to hot-wet environment. J-integral of a central crack in the strengthened beam under three-point bending load was calculated by ABAQUS. In finite element model, simulation of CFL-concrete interface was based on the bilinear cohesive zone model under hot-wet environment and indoor atmosphere. And, then, fatigue crack propagation tests were carried out under high temperature and high humidity (50°C, 95% R · H environment pretreatment and indoor atmosphere (23°C, 78% R · H to obtain a-N curves and crack propagation rate, da/dN, of the strengthened beams. Paris-Erdogan formula was developed based on the numerical analysis and environmental fatigue tests.
Kroon, Martin
2012-01-01
In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of plane stress and steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to examine the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The computational framework builds upon a previous work by the present author (Kroon in Int J Fract 169:49-60, 2011). The model was fully able to predict experimental results in terms of the local surface energy at the crack tip and the total energy release rate at different crack speeds. The predicted distributions of stress and dissipation around the propagating crack tip are presented. The predicted crack tip profiles also agree qualitatively with experimental findings.
Alam, Mohammad Shah
2005-11-01
Structural integrity is the science and technology of the margin between safety and disaster. Proper evaluation of the structural integrity and fatigue life of any structure (aircraft, ship, railways, bridges, gas and oil transmission pipelines, etc.) is important to ensure the public safety, environmental protection, and economical consideration. Catastrophic failure of any structure can be avoided if structural integrity is assessed and necessary precaution is taken appropriately. Structural integrity includes tasks in many areas, such as structural analysis, failure analysis, nondestructive testing, corrosion, fatigue and creep analysis, metallurgy and materials, fracture mechanics, fatigue life assessment, welding metallurgy, development of repairing technologies, structural monitoring and instrumentation etc. In this research fatigue life assessment of welded and weld-repaired joints is studied both in numerically and experimentally. A new approach for the simulation of fatigue crack growth in two elastic materials has been developed and specifically, the concept has been applied to butt-welded joint in a straight plate and in tubular joints. In the proposed method, the formation of new surface is represented by an interface element based on the interface potential energy. This method overcomes the limitation of crack growth at an artificial rate of one element length per cycle. In this method the crack propagates only when the applied load reaches the critical bonding strength. The predicted results compares well with experimental results. The Gas Metal Arc welding processes has been simulated to predict post-weld distortion, residual stresses and development of restraining forces in a butt-welded joint. The effect of welding defects and bi-axial interaction of a circular porosity and a solidification crack on fatigue crack propagation life of butt-welded joints has also been investigated. After a weld has been repaired, the specimen was tested in a universal
Effects of Shot-Peening and Stress Ratio on the Fatigue Crack Propagation of AL 7475-T7351 Specimens
Directory of Open Access Journals (Sweden)
Natália Ferreira
2018-03-01
Full Text Available Shot peening is an attractive technique for fatigue enhanced performance of metallic components, because it increases fatigue crack initiation life prevention and retards early crack growth. Engineering design based on fatigue crack propagation predictions applying the principles of fracture mechanics is commonly used in aluminum structures for aerospace engineering. The main purpose of present work was to analyze the effect of shot peening on the fatigue crack propagation of the 7475 aluminum alloy, under both constant amplitude loading and periodical overload blocks. The tests were performed on 4 and 8 mm thickness specimens with stress ratios of 0.05 and 0.4. The analysis of the shot-peened surface showed a small increase of the micro-hardness values due to the plastic deformations imposed by shot peening. The surface peening beneficial effect on fatigue crack growth is very limited; its main effect is more noticeable near the threshold. The specimen’s thickness only has marginal influence on the crack propagation, in opposite to the stress ratio. Periodic overload blocks of 300 cycles promotes a reduction of the fatigue crack growth rate for both intervals of 7500 and 15,000 cycles.
Temperature dependency of external stress corrosion crack propagation of 304 stainless steel
International Nuclear Information System (INIS)
Hayashibara, Hitoshi; Mizutani, Yoshihiro; Mayuzumi, Masami; Tani, Jun-ichi
2010-01-01
Temperature dependency of external stress corrosion cracking (ESCC) of 304 stainless steel was examined with CT specimens. Maximum ESCC propagation rates appeared in the early phase of ESCC propagation. ESCC propagation rates generally became smaller as testing time advance. Temperature dependency of maximum ESCC propagation rate was analyzed with Arrhenius plot, and apparent activation energy was similar to that of SCC in chloride solutions. Temperature dependency of macroscopic ESCC incubation time was different from that of ESCC propagation rate. Anodic current density of 304 stainless steel was also examined by anodic polarization measurement. Temperature dependency of critical current density of active state in artificial sea water solution of pH=1.3 was similar to that of ESCC propagation rate. (author)
Energy Technology Data Exchange (ETDEWEB)
Seo, Hyeongseok; Baek, Hyungchan; Kim, Hyungyu [Seoul Nat' l Univ. of Sci. and Tech., Seoul (Korea, Republic of)
2014-04-15
In this paper, the effect of cohesive laws on the finite element analysis of crack propagation using cohesive elements is investigated through three-point bending and double cantilever beam problems. The cohesive elements are implemented into ABAQUS/Standard user subroutines(UEL), and the shape of cohesive law is varied by changing parameters in polynomial functions of cohesive traction-separation relations. In particular, crack propagation behaviors are studied by comparing load-displacement curves of the analysis models which have different shapes of cohesive laws with the same values of fracture energy and cohesive strength. Furthermore, the influence of the element size on crack propagation is discussed in this study.
Energy Technology Data Exchange (ETDEWEB)
Hemery, Samuel [Institut PPRIME, CNRS, Université de Poitiers, ISAE ENSMA, UPR 3346, Téléport 2, 1 Avenue Clément Ader, BP 40109, 86961 Futuroscope Chasseneuil Cedex (France); Berdin, Clotilde, E-mail: clotilde.berdin@u-psud.fr [Univ Paris-Sud, SP2M-ICMMO, CNRS UMR 8182, F-91405 Orsay Cedex (France); Auger, Thierry; Bourhi, Mariem [Ecole Centrale-Supelec, MSSMat CNRS UMR 8579, F-92295 Chatenay Malabry Cedex (France)
2016-12-01
Liquid metal embrittlement (LME) of T91 steel is numerically modeled by the finite element method to analyse experimental results in an axisymmetric notched geometry. The behavior of the material is identified from tensile tests then a crack with a constant crack velocity is introduced using the node release technique in order to simulate the brittle crack induced by LME. A good agreement between the simulated and the experimental macroscopic behavior is found: this suggests that the assumption of a constant crack velocity is correct. Mechanical fields during the embrittlement process are then extracted from the results of the finite element model. An analysis of the crack initiation and propagation stages: the ductile fracture probably breaks off the LME induced brittle fracture. - Highlights: • T91 martensitic steel is embrittled by liquid sodium depending on the loading rate at 573 K. • The mechanical behavior is modeled by a von Mises elastic-plastic law. • The LME induced crack propagates at a constant velocity. • The mechanical state at the crack tip does not explain a brittle crack arrest. • The occurrence of the ductile fracture breaks off the brittle fracture.
International Nuclear Information System (INIS)
Masaki, Kiyotaka; Ochi, Yasuo; Matsumura, Takashi; Ikarashi, Takaaki; Sano, Yuji
2010-01-01
Laser peening without protective coating (LPwC) treatment is one of surface enhancement techniques using an impact wave of high pressure plasma induced by laser pulse irradiation. High compressive residual stress was induced by the LPwC treatment on the surface of low-carbon type austenitic stainless steel SUS316L. The affected depth reached about 1mm from the surface. High cycle fatigue tests with four-points rotating bending loading were carried out to confirm the effects of the LPwC treatment on fatigue strength and surface fatigue crack propagation behaviors. The fatigue strength was remarkably improved by the LPwC treatment over the whole regime of fatigue life up to 10 8 cycles. Specimens with a pre-crack from a small artificial hole due to fatigue loading were used for the quantitative study on the effect of the LPwC treatment. The fracture mechanics investigation on the pre-cracked specimens showed that the LPwC treatment restrained the further propagation of the pre-crack if the stress intensity factor range ΔK on the crack tip was less than 7.6 MPa√m. Surface cracks preferentially propagated into the depth direction as predicted through ΔK analysis on the crack by taking account of the compressive residual stresses due to the LPwC treatment. (author)
Biaxial loading effects on the growth of cracks
International Nuclear Information System (INIS)
Brown, M.W.; Miller, K.J.; Walker, T.J.
1983-01-01
Fatigue crack growth under different biaxial stress states is considered for both small scale yielding and high bulk stress conditions. Analytical and elastic finite element results are compared favourably alongside experimental results on a AISI 316 stainless steel at both room and elevated temperatures. Differences in crack growth rates are compared against different crack tip cyclic plastic zone sizes for various degrees of mixed mode loading, thereby overcoming the limitations of the Paris Law and LEFM. The usefulness of the approach is indicated for studies in the behaviour of materials subjected to thermal shock. Where steep temperature gradients are introduced due to rapid thermal transients, high strains are produced which propagate fatigue cracks under cyclic conditions. Since stress gradients are generally associated with thermal shock situations, the cracks grow through a plastically deformed region near the surface into an elastic region. A unified approach to fatigue behaviour, encompassing both linear elastic and elastic-plastic fracture mechanics, will enable analysis of thermal shock situations. The approach to crack propagation developed here shows that cyclic growth rates are a function of a severe strain zone size in which local stresses exceed the tensile strength, i.e. monotonic instability. The effects of stress biaxiality and mixed mode loading are included in the analysis, which may be extended to general yielding situations. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Iqbal, Farasat; Goeken, Mathias [Lehrstuhl Allgemeine Werkstoffeigenschaften, Friedrich-Alexander-Universitaet Erlangen-Nuernberg (Germany); Pyczak, Florian [GKSS Research Centre Geesthacht, Geesthacht (Germany)
2009-07-01
The present study is focused on crack propagation mechanism in Ti-45Al-1Cr and Ti-45Al-5Nb alloys with lamellar microstructure. Atomic force microscopy (AFM) is a versatile technique to study the crack propagation in-situ. AFM was employed to investigate the local deformations near the crack tip. Scanning electron microscopy (SEM) supplements the in-situ observations and was used to get a basic understanding of the crack propagation path over larger distances.A focused ion beam (FIB) was used to investigate the structures and deformation traces underneath the surface. It is concluded that the {gamma}/{alpha}2 interfaces act as favorable sites for new interfacial crack nucleation and also for interlamellar crack propagation. Nucleation of new cracks was often preceded by the interaction of deformation twins with interfaces and also by strong shear band activity in the {gamma}-TiAl lamellae visible as significant surface topography in AFM.Mostly the underneath crack path follows the {gamma}/{alpha}2 interface similar to the situation observed at the surface. The local misorientation measured with electron backscattered diffraction (EBSD) shows {gamma}-lamellae as the region of high deformation as compare to neighboring {alpha}2 -lamellae around the crack tip and its surroundings.
Stress Corrosion Cracking of alloy 600 in high temperature water: a study of mechanisms
International Nuclear Information System (INIS)
Boursier, J.M.; Bouvier, O. de; Gras, J.M.; Noel, D.; Vaillant, F.; Rios, R.
1992-12-01
Investigations of the stress corrosion cracking behaviour of Alloy 600 tubing in high temperature water were performed in order to get a precise knowledge of the different stages of the cracking and their dependence on various parameters. The compatibility of the results with the main mechanisms to be considered was examined. Results showed three stages in the cracking: a true incubation time, a slow-rate propagation period followed by a rapid-propagation stage. Tests separating stress and strain rate contributions show that the strain rate is the main parameter which controls the crack propagation. The hydrogen overpressure was found to increase the crack growth rate up to 1-4 bar, but a strong decrease is observed from 4 to 20 bar. Analysis of the hydrogen ingress in the metal showed that it is neither correlated to the hydrogen overpressure nor to the severity of cracking; so cracking resulting from an hydrogen-model is unlikely. No detrimental effect of oxygen (4 bar) was noticed both in the mill-annealed and the sensitized conditions. Finally, none of the classical mechanisms, neither hydrogen-assisted cracking nor slip-step dissolution, can correctly describe the observed behaviour. Some fractographic examinations, and an influence of primary water on the creep rate of Alloy 600, lead to consider that other recent mechanisms, involving an interaction between dissolution and plasticity, have to be considered
Analysis of interfacial crack propagation under asymmetric loading in anisotropic materials
International Nuclear Information System (INIS)
Pryce, L; Mishuris, G; Morini, L
2013-01-01
This paper considers a steady-state crack propagating along an interface between dissimilar orthotropic materials under an asymmetric load. Although most of the known results so far deal with symmetric loading, it has been shown recently that a significant asymmetry in the applied loading may lead to a pronounced effect in terms of the values of the SIFs. The aim of the paper is to extend these results from the static case to a moving crack. In particular, we show the significance of the asymmetry of the loading for computing the energy release rate
International Nuclear Information System (INIS)
Yang, Xiaoyu
2015-01-01
The purpose of this PhD study is to predict the propagation and arrest of cleavage cracks in a French PWR vessel steel (16MND5). This is accomplished through use of a local criterion based on the critical stress calculated ahead of crack tip. Previous work has shown that fracture mechanism was cleavage associated with the ductile shear zone between the different planes of cracking. Thus, the critical stress at crack tip depends on stain rate. This thesis consists of numerical optimization, identification and validation of a local criterion based on experiments which have complex thermomechanical loads. The criterion accounts for various crack paths, deepening the knowledge about micro mechanisms during crack propagation in order to justify the established criterion. Criterion identification was carried out by using numerical simulations of tension tests performed on CT (Compact Tension) specimens at four different temperatures (-150 C, -125 C, -100 C and -75 C). The eXtended Finite Element Method (X-FEM) was used in CAST3M FE software to model dynamic crack propagation and arrest. The analysis results in 2D and 3D showed that the critical stress at crack tip increased with the inelastic strain rate. Therefore, a criterion based on the critical stress was established. An analytical model was developed to justify the identified criterion. The critical stress given by the local criterion was considered as the sum of the critical cleavage stress and the stress generated by the deformation of ligaments behind the crack tip. In order to quantify this phenomenon, measurements of ligaments' characteristics have been performed on fracture surfaces and on cross-sections of the specimens. The stress profile of the crack lips generated by ligaments was calculated by modeling of multi-cracks on specimen's cross-section. The contribution of stress generated by ligaments to the critical stress at crack tip was obtained with this method, and then the analytical model of
Stepanova, Larisa; Bronnikov, Sergej
2018-03-01
The crack growth directional angles in the isotropic linear elastic plane with the central crack under mixed-mode loading conditions for the full range of the mixity parameter are found. Two fracture criteria of traditional linear fracture mechanics (maximum tangential stress and minimum strain energy density criteria) are used. Atomistic simulations of the central crack growth process in an infinite plane medium under mixed-mode loading using Large-scale Molecular Massively Parallel Simulator (LAMMPS), a classical molecular dynamics code, are performed. The inter-atomic potential used in this investigation is Embedded Atom Method (EAM) potential. The plane specimens with initial central crack were subjected to Mixed-Mode loadings. The simulation cell contains 400000 atoms. The crack propagation direction angles under different values of the mixity parameter in a wide range of values from pure tensile loading to pure shear loading in a wide diapason of temperatures (from 0.1 К to 800 К) are obtained and analyzed. It is shown that the crack propagation direction angles obtained by molecular dynamics method coincide with the crack propagation direction angles given by the multi-parameter fracture criteria based on the strain energy density and the multi-parameter description of the crack-tip fields.
Energy Technology Data Exchange (ETDEWEB)
Silva Diniz, D.; Almeida Silva, A. [Federal University of Campina Grande, Campina Grande-PB (Brazil); Andrade Barbosa, J.M. [Federal University of Pernambuco, Recife-PE (Brazil); Palma Carrasco, J.
2012-05-15
This paper presents a numerical simulation of the effect of hydrogen atomic diffusion on fatigue crack propagation on structural steels. The simulation was performed with a specimen type CT of API 5CT P110 steel, loaded in the tensile opening mode, in plane strain state and under the effects of a cyclic mechanical load and the hydrogen concentration at the crack tip. As hydrogen source, a cathodic protection system was considered, commonly used in subsea pipelines. The equations of evolution of variables at the crack tip form a non-linear system of ordinary differential equations that was solved by means of the 4th order Runge-Kutta method. The solid-solid diffusion through the lattice ahead of the crack tip was simulated using the finite difference method. The simulations results show that under these conditions, the fatigue crack evolution process is enhanced by the hydrogen presence in the material, and that the start time of the crack propagation decreases as its concentration increases. These results show good correlation and consistency with macroscopic observations, providing a better understanding of hydrogen embrittlement in fatigue crack propagation processes in structural steels. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Washabaugh, P. D.; Hill, L. G.
2007-12-01
A dynamic crack propagating in a brittle material releases enough thermal energy to produce visible light. The dynamic fracture of even macroscopically amorphous materials becomes unsteady as the crack propagation velocity approaches the material wave-speeds. The heat generated at a crack-tip, especially as it jumps, may be a mechanism to initiate a self-sustaining reaction in an energetic material. Experiments were conducted in specimens to simulate an infinite plate for ˜10 μs. The initial specimens were 152 mm square by 6 mm thick acrylic sheets, and were fabricated to study non-steady near-wave-speed crack propagation. A variant of this specimen embedded a 25 mm×3 mm PBX 9205 pellet to explore the influence of dynamic Mode-I cracks in these materials. The crack was initiated by up to 0.24 g of Detasheet placed along a precursor 50 mm long notch, with a shield to contain the reaction products and prevent propagation along the fractured surfaces. The crack was studied by means of a streak camera and a Fourier-filter of the light reflecting off the newly minted surfaces. The sub-microsecond behavior of holes initiating, preceding and coalescing with the main crack were observed in the PMMA samples. The embedding and mechanical loading of explosives by this technique did not initiate a self-sustaining reaction in preliminary testing.
Effect of Layering on Cracking Initiation and Propagation under Uniaxial Compression
Modiriasari, A.; Jiang, L.; Yoon, H.; Bobet, A.; Pyrak-Nolte, L. J.
2017-12-01
Rock anisotropy can arise from textural and structural causes both of which contribute to anisotropic strength and moduli. Rock variability makes it difficult to determine which properties dominate failure. Here, laboratory experiments were performed on 3D printed samples to examine the effect of layering on crack formation. Samples with two pre-existing coplanar flaws were fabricated using an additive 3D printing process (Projet CJP 360). Layers of gypsum (0.2 mm thick) were printed in either a horizontal (H) or a vertical (V) orientation to create prismatic samples (152.4 mm x 76.2 mm x 25.1 mm) with two 12.7 mm long coplanar flaws (19.05 mm apart) oriented at 450 with the load. Cracks were induced under uniaxial loading conditions. Digital image correlation (DIC) and acoustic emission (AE) (18 AE sensors with a frequency range of 100-450 kHz) were used to monitor crack evolution. DIC imaging of the V specimen during uniaxial compression showed that smooth cracks were initiated and propagated from the tips of the flaws parallel to the layering. Unlike the strongly bonded samples, no cracks were formed between the pre-existing flaws. The failure mechanism between the flaws was controlled by the weak bonding between the layers, and not by the coalescence of the new cracks. However, for the H specimen, failure was caused by crack coalescence between the two flaws. The new cracks exhibited a step-like roughness that was influenced by the layering in the sample. AE events were only detected when a synchronized mode was used. 3D printed samples can be effectively used to study the effect of anisotropic layering on crack initiation and propagation in a repeatable and controlled manner. Acknowledgements: Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security
Probabilistic aspects of fatigue crack propagation data for zirconium-2.5 % niobium
International Nuclear Information System (INIS)
Wilkins, B.J.S.; Reich, A.R.
1976-11-01
Fatigue crack propagation data for Zr-2.5 % Nb pressure tube material at 20 and 400 deg C are presented. The practical application of these data in terms of error analysis and extrapolation errors is discussed. (author)
Crack Behaviour in Laminar Ceramics with Strong Interfaces
Czech Academy of Sciences Publication Activity Database
Náhlík, Luboš; Šestáková, Lucie; Hutař, Pavel
2010-01-01
Roč. 417-418, - (2010), s. 301-304 ISSN 1013-9826 R&D Projects: GA AV ČR(CZ) KJB200410803; GA ČR GA106/09/0279 Institutional research plan: CEZ:AV0Z20410507 Keywords : ceramic laminate * crack propagation direction * residual stress * flaw tolerant ceramic Subject RIV: JL - Materials Fatigue, Friction Mechanics
Creep-fatigue behaviour of the titanium alloy IMI 834 at 600 C
International Nuclear Information System (INIS)
Nowack, H.; Kordisch, T.
1998-01-01
In the present study the creep-fatigue behaviour of the titanium alloy IMI 834 at 600 C was investigated. A comparison of the crack initiation life behaviour and of the crack propagation as caused by different types of complex creep-fatigue cycles (with hold times into tension and/or into compression direction and with different loading rates into tension and/or into compression direction) showed, that a slow increase of the loadings into tension reduced the life and increased the crack velocity more than hold times at the maximum load. Furthermore, there existed environmental influences. On the basis of the experimental investigations the prediction capability of convenient crack initiation life prediction methods was evaluated. It turned out that the prediction capability of the strain range partitioning method could be improved if it was frequency modified. The prediction capability of the frequency modification method could also be improved, if mean stresses in the cycles were explicitely accounted for. In the short and long crack stage the propagation behaviour could be correlated well if the effective cyclic J-integral was used. This is of importance for damage tolerance considerations. Because the strains and the stresses at the crack tip are most important for the crack propagation behaviour, they were analysed on the basis of the finite element method. It was found that the strains and stresses differed for different types of creep-fatigue cycles. (orig.)
International Nuclear Information System (INIS)
Romaniv, O.N.; Nikiforchin, G.N.; Tsirul'nik, A.T.
1984-01-01
The 40 Kh steel is taken as an example to investigate the dependence of electrochemical parameters in the crack tip and characteristics of corrosion static cracking resistance of martensitic steel on the composition of environment. The tests are performed in acidic and alkaline solutions prepared by adding HC or NaOH in distilled water. It is established that growth of pH value of initial solutions trom 0 to 13 brings about linear increase of a threshold stress intensity factor. It is found that acidic medium in the crack tip preserves up to pH 13 of initial medium. The possibility of corrosion crack propagation in alkaline solutions according to the mechanism of hydrogen embrittlement is proved
International Nuclear Information System (INIS)
Curtit, F.
2000-01-01
This study realised in LISN Laboratory of CEA Saclay, deals with the creep fatigue propagation of semi elliptical crack at the temperature of 650 deg C in 316L(N) stainless steel plates with or without welded joints. A vast majority of the studies on creep fatigue propagation models are based on specimen (CT) especially designed for crack propagation study. The PLAQFLU program performed in LISN laboratory deals with the application and adaptation of these models to complex crack shape, which are more representative of the cracks observed in industrial components. In this scope, we use propagation tests realised at the temperature of 650 deg C with wide plates containing semi elliptical defects. For some of them, the initial defect is machined in the middle of a welded joint, which constitute a privileged site for the crack initiation. The approach used in this study is based on global parameters of fracture mechanics. At first, tests on CT specimen are used in order to determine the propagation laws correlating the crack growth rate to the global parameters K or C * . These laws are then supposed to be intrinsic to our materials and are used to analysed the semi elliptical crack propagation. The analysis of the comportment of the crack during the hold time demonstrates the possibility to establish a correlation between the crack propagation both in the deepest and the surface point and the local value of C * . These correlations are coherent in the different points of the crack front for the different applied hold times, and they present a reasonably good agreement with the creep propagation law identified on CT specimen. The simulation of test performed on based metal specimen with a model of summation of both creep and pure fatigue crack growth gives acceptable results when the calculus of the simplified expression of C * s considers a continuous evolution of creep deformations rate during the all test. (author)
Simulation of crack propagation in steel plate with strain softening model
Energy Technology Data Exchange (ETDEWEB)
Chan, O.B.; Elwi, A.E.; Grondin, G.Y.
2006-05-15
A new material model for simulating the fracture behaviour of structural steel was presented. Recent research on crack initiation and continuum damage mechanics was presented. A modified continuum damage model was also evaluated. Strain softening elements were then used to simulate material cracks in a steel structure. The analysis then compared load versus displacement and load versus clip-gauge displacement curves from various different experimental and numerical studies. A finite element analysis technique was used to simulate the fracture behaviour of 3-points bending specimens. Results of the analysis showed that the model predicted 90 per cent of the load and stress intensity factor at fracture initiation. A BE 365 electric shovel boom was used in the study to simulate fracture behaviour. Coupon test specimens were used to validate analysis predictions. It was concluded that the model was able to reduce the stiffness of the boom when the softening element reached yield strength limits during fracture initiation. 29 refs., 12 tabs., 58 figs.
Czech Academy of Sciences Publication Activity Database
Malíková, L.; Veselý, V.; Seitl, Stanislav
2015-01-01
Roč. 9, č. 33 (2015), s. 25-32 ISSN 1971-8993 Institutional support: RVO:68081723 Keywords : Near-crack-tip fields * Williams expansion * Crack propagation direction * Multi-parameter fracture criteria * Finite element analysis Subject RIV: JL - Materials Fatigue, Friction Mechanics
Prediction of crack propagation in layered ceramics with strong interfaces
Czech Academy of Sciences Publication Activity Database
Náhlík, Luboš; Šestáková, L.; Hutař, Pavel; Bermejo, R.
2010-01-01
Roč. 77, č. 11 (2010), s. 2192-2199 ISSN 0013-7944 R&D Projects: GA AV ČR(CZ) KJB200410803; GA ČR GA101/09/1821 Institutional research plan: CEZ:AV0Z20410507 Keywords : Ceramic laminate * Crack propagation direction * Residual stress * Flaw tolerant ceramics * Optimal design Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.571, year: 2010
A Property of Crack Propagation at the Specimen of CFRP with Layer Angle
Energy Technology Data Exchange (ETDEWEB)
Hwang, Gue Wan; Cho, Jae Ung [Kongju Univ., Kongju (Korea, Republic of); Cho, Chong Du [Inha Univ., Incheon (Korea, Republic of)
2016-12-15
CFRP is the composite material manufactured by the hybrid resin on the basis of carbon fiber. As this material has the high specific strength and the light weight, it has been widely used at various fields. Particularly, the unidirectional carbon fiber can be applied with the layer angle. CFRP made with layer angle has the strength higher than with no layer angle. In this paper, the property of crack growth due to each layer angle was investigated on the crack propagation and fracture behavior of the CFRP compact tension specimen due to the change of layer angle. The value of maximum stress is shown to be decreased and the crack propagation is slowed down as the layer angle is increased. But the limit according to the layer angle is shown as the stress is increased again from the base point of the layer angle of 60°.This study result is thought to be utilized with the data which verify the probability of fatigue fracture when the defect inside the structure at using CFRP of mechanical structure happens.
A Property of Crack Propagation at the Specimen of CFRP with Layer Angle
International Nuclear Information System (INIS)
Hwang, Gue Wan; Cho, Jae Ung; Cho, Chong Du
2016-01-01
CFRP is the composite material manufactured by the hybrid resin on the basis of carbon fiber. As this material has the high specific strength and the light weight, it has been widely used at various fields. Particularly, the unidirectional carbon fiber can be applied with the layer angle. CFRP made with layer angle has the strength higher than with no layer angle. In this paper, the property of crack growth due to each layer angle was investigated on the crack propagation and fracture behavior of the CFRP compact tension specimen due to the change of layer angle. The value of maximum stress is shown to be decreased and the crack propagation is slowed down as the layer angle is increased. But the limit according to the layer angle is shown as the stress is increased again from the base point of the layer angle of 60°.This study result is thought to be utilized with the data which verify the probability of fatigue fracture when the defect inside the structure at using CFRP of mechanical structure happens
Directory of Open Access Journals (Sweden)
Taha Özyürek
2017-11-01
Full Text Available Objectives To determine the incidence of crack formation and propagation in apical root dentin after retreatment procedures performed using ProTaper Universal Retreatment (PTR, Mtwo-R, ProTaper Next (PTN, and Twisted File Adaptive (TFA systems. Materials and Methods The study consisted of 120 extracted mandibular premolars. One millimeter from the apex of each tooth was ground perpendicular to the long axis of the tooth, and the apical surface was polished. Twenty teeth served as the negative control group. One hundred teeth were prepared, obturated, and then divided into 5 retreatment groups. The retreatment procedures were performed using the following files: PTR, Mtwo-R, PTN, TFA, and hand files. After filling material removal, apical enlargement was done using apical size 0.50 mm ProTaper Universal (PTU, Mtwo, PTN, TFA, and hand files. Digital images of the apical root surfaces were recorded before preparation, after preparation, after obturation, after filling removal, and after apical enlargement using a stereomicroscope. The images were then inspected for the presence of new apical cracks and crack propagation. Data were analyzed with χ2 tests using SPSS 21.0 software. Results New cracks and crack propagation occurred in all the experimental groups during the retreatment process. Nickel-titanium rotary file systems caused significantly more apical crack formation and propagation than the hand files. The PTU system caused significantly more apical cracks than the other groups after the apical enlargement stage. Conclusions This study showed that retreatment procedures and apical enlargement after the use of retreatment files can cause crack formation and propagation in apical dentin.
Özyürek, Taha; Tek, Vildan; Yılmaz, Koray; Uslu, Gülşah
2017-11-01
To determine the incidence of crack formation and propagation in apical root dentin after retreatment procedures performed using ProTaper Universal Retreatment (PTR), Mtwo-R, ProTaper Next (PTN), and Twisted File Adaptive (TFA) systems. The study consisted of 120 extracted mandibular premolars. One millimeter from the apex of each tooth was ground perpendicular to the long axis of the tooth, and the apical surface was polished. Twenty teeth served as the negative control group. One hundred teeth were prepared, obturated, and then divided into 5 retreatment groups. The retreatment procedures were performed using the following files: PTR, Mtwo-R, PTN, TFA, and hand files. After filling material removal, apical enlargement was done using apical size 0.50 mm ProTaper Universal (PTU), Mtwo, PTN, TFA, and hand files. Digital images of the apical root surfaces were recorded before preparation, after preparation, after obturation, after filling removal, and after apical enlargement using a stereomicroscope. The images were then inspected for the presence of new apical cracks and crack propagation. Data were analyzed with χ 2 tests using SPSS 21.0 software. New cracks and crack propagation occurred in all the experimental groups during the retreatment process. Nickel-titanium rotary file systems caused significantly more apical crack formation and propagation than the hand files. The PTU system caused significantly more apical cracks than the other groups after the apical enlargement stage. This study showed that retreatment procedures and apical enlargement after the use of retreatment files can cause crack formation and propagation in apical dentin.
International Nuclear Information System (INIS)
Ide, Hiroshi; Matsui, Yoshinori; Kawamata, Kazuo; Taguchi, Taketoshi; Kanazawa, Yoshiharu; Onuma, Yuichi; Watanabe, Hiroyuki; Inoue, Shuichi; Izumo, Hironobu; Ishida, Takuya; Saito, Takashi; Ishitsuka, Etsuo; Kawamura, Hiroshi; Kaji, Yoshiyuki; Ugachi, Hirokazu; Tsukada, Takashi
2008-03-01
It is known that irradiation Assisted Stress Corrosion Cracking (IASCC) occurs when austenitic stainless steel components used for light water reactor (LWR) are irradiated for a long period. In order to evaluate the high aging of the nuclear power plant, the study of IASCC becomes the important problem. The specimens irradiated in the reactor were evaluated by post irradiation examination in the past study. For the appropriate evaluation of IASCC, it is necessary to test it under the simulated LWR conditions; temperature, water chemistry and irradiation conditions. In order to perform in-pile SCC test, saturated temperature capsule (SATCAP) was developed. There are crack growth test, crack propagation test and so on for in-pile SCC test. In this report, SATCAP for crack propagation test is reported. (author)
On the calculation of crack propagation behavior in disks and plates using a mixed finite method
International Nuclear Information System (INIS)
Fischer, W.
1991-01-01
According to the linear theory of elasticity, infinitely high stresses occur in the crack tips of cracked components. Plastic flow initiation or previous damage, however, will limit these stress singularities to an upper maximum stress for all real materials. To permit acquisition of this highly localized material behavior, while avoiding a very high physical nonlinear calculation effort for the evaluation of crack propagation behavior in disks and plates, models essentially based on Dugdale and Barenblatt are used. This involves determining the stress and displacement conditions required for the simulation of crack propagation by means of a mixed finite method introducing the disk cutting forces and plate curvatures or moments as unknown quantities. In addition to pure disk and plate problems, also coupled disk-plate problems are covered, where the coupling, on one hand, is due to the consideration of high deformations. (orig.) With 66 figs., 8 tabs [de
International Nuclear Information System (INIS)
Bareiss, J.; Maile, K.; Berger, C.; Mayer, K.H.; Weiss, M.
1994-01-01
The results available so far have shown that under vibration stress at room temperature and at 530 C, the simplified equations of fracture mechanics are sufficient (in spite of the complicated fault geometries), in order to conservatively describe the behaviour of fault positions (open or partly-healed hot cracks) with regard to their crack initiation behaviour if combined with the findings US test technique. Here the sample castings which in the initial state showed fault indications of US type EET near the surface, tend to earlier initiation of a crack compared to lower fault positions of the samples. Internal fault positions (partially healed hot cracks) often only showed local cracks (trans-crystalline deformation cracks) within the fault area with an order of magnitude of about 10-50 μm, in spite of exceeding the threshold value Δ Ko. The comparison of the crack propagation behaviour of the sample castings, determined via the potential sensor method on medium lengths of fault with the results of crack growth of fracture mechanics samples in the da/dN- Δ K diagram showed for the evaluated sample castings with a relatively great initial depth or length of fault that the upper scatter band limit of the Paris Law determined for the material can be used to estimate the fault position behaviour. (orig./RHM) [de
Hai-Yang, Song; Yu-Long, Li
2016-02-01
The effects of amorphous lamella on the crack propagation behavior in crystalline/amorphous (C/A) Mg/Mg-Al nanocomposites under tensile loading are investigated using the molecular dynamics simulation method. The sample with an initial crack of orientation [0001] is considered here. For the nano-monocrystal Mg, the crack growth exhibits brittle cleavage. However, for the C/A Mg/Mg-Al nanocomposites, the ‘double hump’ behavior can be observed in all the stress-strain curves regardless of the amorphous lamella thickness. The results indicate that the amorphous lamella plays a critical role in the crack deformation, and it can effectively resist the crack propagation. The above mentioned crack deformation behaviors are also disclosed and analyzed in the present work. The results here provide a strategy for designing the high-performance hexagonal-close-packed metal and alloy materials. Project supported by the National Natural Science Foundation of China (Grant Nos. 11372256 and 11572259), the 111 Project (Grant No. B07050), the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-12-1046), and the Program for New Scientific and Technological Star of Shaanxi Province, China (Grant No. 2012KJXX-39).
Washabaugh, Peter; Hill, Larry
2007-06-01
A dynamic crack propagating in a brittle material releases enough thermal energy to produce visible light. The dynamic fracture of even macroscopically amorphous materials becomes unsteady as the crack propagation velocity approaches the material wave-speeds. The heat generated at a crack-tip, especially as it jumps, may be a mechanism to initiate a self-sustaining reaction in an energetic material. Experiments were conducted in specimens to simulate an infinite plate for 20 μs. The initial specimens were 152 mm square by 6 mm thick acrylic sheets, and were fabricated to study non-steady near-wave-speed crack propagation. A variant of this specimen embedded a 25 mm x 3 mm PBX 9205 pellet to explore the influence of dynamic Mode-I cracks in these materials. The crack was initiated by up to 0.2 g of Detasheet placed along a precursor 50 mm long notch, with a shield to contain the reaction products and prevent propagation along the fractured surfaces. The crack was studied by means of a streak camera and a Fourier-filter of the light reflecting off the newly minted surfaces. The sub-microsecond behavior of holes initiating, preceding and coalescing with the main crack were observed in the PMMA samples. The embedding and mechanical loading of explosives by this technique did not initiate a self-sustaining reaction in preliminary testing.
Energy Technology Data Exchange (ETDEWEB)
Soppa, Ewa Anna; Silcher, Horst
2015-01-31
Fatigue crack growth of short and long cracks was investigated for both materials: the Nb-stabilized austenitic stainless steel X6 CrNiNb 18-10 and the ferritic-bainitic steel 22 NiMoCr 3-7. These both steels belong to the materials in the primary circuit of german power plants. For a reliable estimation of the lifetime of components subject to cyclic fatigue a detailed knowledge of the phenomena accompanying fatigue processes and which cause both - initiation and growth of fatigue cracks is essential. The deformation induced transformation of austenite into α'-martensite at room temperature is thus very important in the initiation and growth of fatigue cracks. Because these processes are manifest at first at the microlevel, the use of methods which reveal information at high resolution is of significant importance. In order to study the initiation and growth of short cracks, cylindrical smooth specimens, compact tension C(T)- and modified C(T)-specimens have been used. Cyclic crack propagation of long cracks was investigated on compact tension C(T)-specimens with W=50 mm and B=10 mm. The SEM, TEM and EBSD technique are powerful methods for determining crystallographic orientation, for the identification of individual phases and for recealing plastic deformation. They were used for analyses of microcracks in combination with interrupted cyclic tests. The impact of crack closure on the threshold parameter ΔK{sub th} and the crack growth rate da/dN was investigated experimentally for the growth of long cracks under cyclic loading for different R-values at room temperature. Additional tests were performed at T=288 C in order to investigate the role of temperature on crack growth rates. The effect of overloads in tension and compression as another factor influencing the crack growth was also studied. Measured crack growth curves were fitted using Paris and Erdogan-Ratwani law as well as the NASGRO-equation. Fracture surfaces of selected specimens for both steels
International Nuclear Information System (INIS)
Baer, K.K.O.; Kleist, G.; Nickel, H.
1991-03-01
The aim of this work is the clearification of R-curve behaviour of non-transforming ceramics, in particular aluminum oxide exhibiting incrystalline fracture. Investigations of crack growth in controlled bending experiments were performed using 3-Pt- and 4-Pt-bending samples of differing sizes under inert conditions. The fracture experiments were realized using several loading techniques, for example constant and varying displacement rates, load rupture (P = 0) and relaxation tests (v = 0). In addition unloading and reloading experiments were performed to investigate hysteresis curves and residual displacements in accordance with R-curve behaviour. During the crack-growth experiments, the crack extension was measured in situ using a high resolution immersion microscope. With this technique, the fracture processes near the crack tip (crack activity zone) was observed as well. The crack resistance as a function of crack extension (R-curve) was determined using differing calculation methods. All of the methods used resulted in approximately identical R-curves, within the statistical error band. The crack resistance at initiation R 0 was 20 N/m. The crack resistance increased during approximately 3 mm of growth to a maximum of 90 N/m. A decrease in the crack resistance was determined for large a/W (crack length normalized with sample height) values, independant of the calculation methods. The R-curve behaviour was interpreted as due to a functional resistance behind the observed crack tip, which arises from a volume dilatation in the crack activity zone while the crack proceeds. (orig.) [de
Directory of Open Access Journals (Sweden)
Ding Jun
2014-01-01
Full Text Available This paper reports a numerical simulation procedure to model crack propagation in TGO layer and TGO growth near a surface groove in metal substrate upon multiple thermal-mechanical cycles. The material property change method is employed to model TGO formation cycle by cycle, and the creep properties for constituent materials are also incorporated. Two columns of repeated nodes are placed along the interface of the potential crack, and these nodes are bonded together as one node at a geometrical location. In terms of critical crack opening displacement criterion, onset of crack propagation in TGO layer has been determined by finite element analyses in comparison with that without predefined crack. Then, according to the results from the previous analyses, the input values for the critical failure parameters for the subsequent analyses can be decided. The robust capabilities of restart analysis in ABAQUS help to implement the overall simulation for TGO crack propagation. The comparison of the TGO final deformation profile between numerical and experimental observation shows a good agreement indicating the correctness and effectiveness of the present procedure, which can guide the prediction of the failure in TGO for the future design and optimization for TBC system.
Qin, Ming; Li, Jianfeng; Chen, Songying; Qu, Yanpeng
FV520B steel is a kind of precipitation hardening Martensitic stainless steel, it has high-strength, good plasticity and good corrosion resistance. Stress corrosion cracking (SCC) is one of the main corrosion failure mode for FV520B in industrial transportation of natural gas operation. For a better understanding the effect on SCC of FV520B, the improved wedge opening loading (WOL) specimens and constant displacement loading methods were employed in experimental research in carbon dioxide and hydrogen sulfide solution. The test results showed that the crack propagation rate is 1.941 × 10-7-5.748 × 10-7 mm/s, the stress intensity factor KISCC is not more than 36.83 MPa √{ m } . The rate increases with the increasing of the crack opening displacement. Under the condition of different initial loading, KISCC generally shows a decreasing tendency with the increase in H2S concentration, and the crack propagation rate showed an increasing trend substantially. For the enrichment of sulfur ion in the crack tip induced the generation of pitting corrosion, promoting the surrounding metal formed the corrosion micro batteries, the pit defects gradually extended and connected with the adjacent pit to form a small crack, leading to further propagation till cracking happened. Fracture microscopic morphology displayed typical brittle fracture phenomena, accompanying with trans-granular cracking, river shape and sector, many second cracks on the fracture surface.
International Nuclear Information System (INIS)
Cirimelo, Pablo G.
2002-01-01
In the present thesis work the propagation of cracks due to the delayed hydride cracking (DHC) mechanism in Zr-2,5 % Nb pressure tubes is analyzed. For this purpose two different type of tubes of different origin were used: CANDU type (Canada) and RBMK type (Russia). The analyzed figurative parameters were: critical temperature Tc (highest temperature at which DHC phenomenon could occur) and crack propagation velocity by DHC, Vp, in the axial direction. The influence of the memory effect (phenomenon proper of hydride precipitation) was studied, as well as the type of cracks (fatigue or DHC) on Tc. However, no influence of these effects was found. Instead, it was found that Tc varies with the hydrogen content of the specimen, in agreement with previous works. Samples obtained from tubes with different microstructures and similar amounts of hydrogen presented similar Tc values. It was also shown that DHC propagation could occur without precipitated hydrides in the volume. Besides, Vp determinations were performed in temperature ranges and hydrogen amounts of technological importance. Two techniques were set up in order to determine Vp at different temperatures in a single specimen, thus saving time and material. An Arrhenius type variation was found for Vp vs. temperature, for temperatures lower than that corresponding to precipitation. For higher temperatures, but lower than the critical one, velocity decreases with temperature. Determination of Vp vs. temperature was performed for the two above-mentioned materials, whose microstructure and hardness were previously characterized. For RBMK material, which presents a spheroidal β phase, the velocity was lower than the corresponding to CANDU material, in which β phase is formed by continuous plates. In addition, yield stress σ Y is lower in RBMK material, which presents lower Vp. However, it is considered that the effect of microstructure is more important on Vp since it highly affects diffusion of hydrogen from the
Directory of Open Access Journals (Sweden)
Ming Qin
Full Text Available FV520B steel is a kind of precipitation hardening Martensitic stainless steel, it has high-strength, good plasticity and good corrosion resistance. Stress corrosion cracking (SCC is one of the main corrosion failure mode for FV520B in industrial transportation of natural gas operation. For a better understanding the effect on SCC of FV520B, the improved wedge opening loading (WOL specimens and constant displacement loading methods were employed in experimental research in carbon dioxide and hydrogen sulfide solution. The test results showed that the crack propagation rate is 1.941 × 10−7–5.748 × 10−7 mm/s, the stress intensity factor KISCC is not more than 36.83 MPa m. The rate increases with the increasing of the crack opening displacement. Under the condition of different initial loading, KISCC generally shows a decreasing tendency with the increase in H2S concentration, and the crack propagation rate showed an increasing trend substantially. For the enrichment of sulfur ion in the crack tip induced the generation of pitting corrosion, promoting the surrounding metal formed the corrosion micro batteries, the pit defects gradually extended and connected with the adjacent pit to form a small crack, leading to further propagation till cracking happened. Fracture microscopic morphology displayed typical brittle fracture phenomena, accompanying with trans-granular cracking, river shape and sector, many second cracks on the fracture surface. Keywords: FV520B, Wedge opening loading specimen, Stress corrosion cracking, Hydrogen sulfide
Mechanical behaviour of cracked welded structures including mismatch effect
International Nuclear Information System (INIS)
Hornet, P.
2002-01-01
The most important parameters for predicting more precisely the fracture behaviour of welded structures have been identified. In particular, the plasticity development at the crack tip in the ligament appeared as a major parameter to evaluate the yield load of such a complex structure. In this way defect assessments procedures have been developed or modified to take into account the mismatch effect that is to say the mechanical properties of the different material constituting the weld joint. This paper is a synthesis of the work done in the past at Electricite de France on this topic in regards with other work done in France or around the World. The most important parameters which control the plasticity development at the crack tip and so mainly influence the fracture behaviour of welded structures are underlined: the mismatch ratio (weld to base metal yield strength ratio), the mismatch ratio (weld to base metal yield strength ratio), the ligament size and the weld width. Moreover, commonly used fracture toughness testing procedures developed in case of homogeneous specimens cannot be used in a straight forward manner and so has to be modified to take into account the mismatch effect. Number or defect assessment procedures taking into account the mismatch effect by considering the yield load of the welded structure are shortly described. Then, the 'Equivalent Material Method' developed at EDF which allows a good prediction of the applied J-Integral at the crack tip is more detailed. This procedure includes not only both weld and base metal yield strength, the structure geometry, the crack size and the weld dimension using the yield load of the real structures but also includes the effect of both weld and base metal strain hardening exponents. Some validations of this method are proposed. Finally, the ability of finite element modelling to predict the behaviour of such welded structures is demonstrated by modelling real experiments: crack located in the middle of
Snider, H. L.; Reeder, F. L.; Dirkin, W. J.
1972-01-01
Fourteen C-130 airplane center wings, each containing service-imposed fatigue damage resulting from 4000 to 13,000 accumulated flight hours, were tested to determine their fatigue crack propagation and static residual strength characteristics. Eight wings were subjected to a two-step constant amplitude fatigue test prior to static testing. Cracks up to 30 inches long were generated in these tests. Residual static strengths of these wings ranged from 56 to 87 percent of limit load. The remaining six wings containing cracks up to 4 inches long were statically tested as received from field service. Residual static strengths of these wings ranged from 98 to 117 percent of limit load. Damage-tolerant structural design features such as fastener holes, stringers, doublers around door cutouts, and spanwise panel splices proved to be effective in retarding crack propagation.
International Nuclear Information System (INIS)
Choi, Seon Soon
2012-01-01
The primary aim of this paper was to evaluate several probabilistic fatigue crack propagation models using the residual of a random variable, and to present the model fit for probabilistic fatigue behavior in Mg Al Zn alloys. The proposed probabilistic models are the probabilistic Paris Erdogan model, probabilistic Walker model, probabilistic Forman model, and probabilistic modified Forman models. These models were prepared by applying a random variable to the empirical fatigue crack propagation models with these names. The best models for describing fatigue crack propagation models with these names. The best models for describing fatigue crack propagation models with these names. The best models for describing fatigue crack propagation models with these names. The best models vor describing fatigue crack propagation behavior in Mg Al Zn alloys were generally the probabilistic Paris Erdogan and probabilistic Walker models. The probabilistic Forman model was a good model only for a specimen with a thickness of 9.45mm
Yamamoto, Takatsugu; Ferracane, Jack L; Sakaguchi, Ronald L; Swain, Michael V
2009-04-01
Polymerization contraction of dental composite produces a stress field in the bonded surrounding substrate that may be capable of propagating cracks from pre-existing flaws. The objectives of this study were to assess the extent of crack propagation from flaws in the surrounding ceramic substrate caused by composite contraction stresses, and to propose a method to calculate the contraction stress in the ceramic using indentation fracture. Initial cracks were introduced with a Vickers indenter near a cylindrical hole drilled into a glass-ceramic simulating enamel. Lengths of the radial indentation cracks were measured. Three composites having different contraction stresses were cured within the hole using one- or two-step light-activation methods and the crack lengths were measured. The contraction stress in the ceramic was calculated from the crack length and the fracture toughness of the glass-ceramic. Interfacial gaps between the composite and the ceramic were expressed as the ratio of the gap length to the hole perimeter, as well as the maximum gap width. All groups revealed crack propagation and the formation of contraction gaps. The calculated contraction stresses ranged from 4.2 MPa to 7.0 MPa. There was no correlation between the stress values and the contraction gaps. This method for calculating the stresses produced by composites is a relatively simple technique requiring a conventional hardness tester. The method can investigate two clinical phenomena that may occur during the placement of composite restorations, i.e. simulated enamel cracking near the margins and the formation of contraction gaps.
Effects of pulse current stimulation on the thermal fatigue crack propagation behavior of CHWD steel
International Nuclear Information System (INIS)
Lin, H.Q.; Zhao, Y.G.; Gao, Z.M.; Han, L.G.
2008-01-01
The fatigue crack propagating behaviors of cast hot working die (CHWD) steel untreated and treated by an electric current in the intermediate stage of thermal fatigue were investigated in the present study. The circle/elliptical heating affected zone (HAZ) was formed ahead of the notch tip on the fatigued specimens after pulse electric current stimulation. Both SEM observation and X-ray diffraction analysis revealed that pulse electric current stimulation refined grains/subgrains in the HAZs. With the prolonging of discharging duration, the grains/subgrains decreased in size and the dislocation density and microhardness increased gradually. The grain refinement and dislocation density increase played an important role in the material strengthening, which inevitably enhanced the propagation resistance and delayed the propagation of thermal fatigue cracks. Therefore, the pulse electric current stimulation was an effective method to improve the service lifetime of die material
Crack propagation behavior of Ti-5Ta alloy in boiling nitric acid solution
International Nuclear Information System (INIS)
Motooka, Takafumi; Kiuchi, Kiyoshi
1999-05-01
The crack propagation behavior of Ti-5Ta alloy both in boiling nitric acid solution and in air at room temperature has been investigated. The crack growth rate of Ti-5Ta alloy was measured as a function of the stress intensity factor range. After the tests, the fracture surface morphology was observed by a scanning electron microscope and the crystallographic orientation was examined by X-ray diffraction analysis. Difference in the crack growth behavior was not observed in both environments. The crack growth rate in boiling nitric acid solution was similar to that in air at room temperature. Moreover, the crystallographic orientation of Ti-5Ta alloy had little effect on the fatigue behavior, because this alloy does not have the susceptibility to SCC in nitric acid solution. (author)
Predominantly elastic crack growth under combined creep-fatigue cycling
International Nuclear Information System (INIS)
Lloyd, G.J.
1979-01-01
A rationalization of the various observed effects of combined creep-fatigue cycling upon predominantly elastic fatigue-crack propagation in austenitic steel is presented. Existing and new evidence is used to show two main groups of behaviour: (i) material and cycling conditions which lead to modest increases (6-8 times) in the rate of crack growth are associated with relaxation-induced changes in the material deformation characteristics, and (ii) material and cycling conditions severe enough to generate internal fracture damage lead to significant (up to a factor of 30) increases in crack growth rate when compared with fast-cycling crack propagation rates at the same temperature. A working hypothesis is presented to show that the boundary between the two groups occurs when the scale of the nucleated creep damage is of the same magnitude as the crack tip opening displacement. This leads to the possibility of unstable crack advance. Creep crack growth rates are shown to provide an upper bound to creep-fatigue crack growth rates when crack advance is unstable. If the deformation properties only are affected by the creep-fatigue cycling then creep crack growth rates provide a lower bound. The role of intergranular oxygen corrosion in very low frequency crack growth tests is also briefly discussed. (author)
International Nuclear Information System (INIS)
Morgeneyer, T.F.; Helfen, L.; Sinclair, I.; Proudhon, H.; Xu, F.; Baumbach, T.
2011-01-01
Ductile crack initiation and propagation within a naturally aged aluminium alloy sheet has been observed in situ via synchrotron radiation-computed laminography, a technique specifically adapted to three-dimensional imaging of thin objects that are laterally extended. Voids and intermetallic particles, and their subsequent evolution during ductile crack extension at different associated levels of stress triaxiality, were clearly observed within fracture coupons of a reasonable engineering length-scale, overcoming the conventional sample size limitation of computed tomography at high resolutions.
Energy Technology Data Exchange (ETDEWEB)
Kabiri, M.R
2003-12-01
This study was performed at Centre des Materiaux de l'Ecole des Mines de Paris. It deals with identification and transferability of high temperature creep cracking laws of steels. A global approach, based on C{sup *} and J non-linear fracture mechanics parameters has been used to characterize creep crack initiation and propagation. The studied materials are: the ferritic steels 1Cr-1Mo-1/4V (hot and cold parts working at 540 and 250 C) used in the thermal power stations and the austenitic stainless steel 316 L(N) used in the nuclear power stations. During this thesis a data base was setting up, it regroups several tests of fatigue, creep, creep-fatigue, and relaxation. Its particularity is to contain several creep tests (27 tests), achieved at various temperatures (550 to 650 C) and using three different geometries. The relevance of the C{sup *} parameter to describe the creep crack propagation was analysed by a means of systematic study of elasto-viscoplastic stress singularities under several conditions (different stress triaxiality). It has been shown that, besides the C{sup *} parameter, a second non singular term, denoted here as Q{sup *}, is necessary to describe the local variables in the vicinity of the crack tip. Values of this constraint parameter are always negative. Consequently, application of typical creep crack growth laws linking the creep crack growth rate to the C{sup *} parameter (da/dt - C{sup *}), will be conservative for industrial applications. Furthermore, we showed that for ferritic steels, crack incubation period is important, therefore a correlation of Ti - C{sup *} type has been kept to predict crack initiation time Ti. For the austenitic stainless steel, the relevant stage is the one of the crack propagation, so that a master curve (da/dt - C{sup *}), using a new data analysis method, was established. Finally, the propagation of cracks has been simulated numerically using the node release technique, allowing to validate analytical
Energy Technology Data Exchange (ETDEWEB)
Ancelet, O
2005-07-01
The incident which has occurred on the Civaux power plant has shown the noxiousness of thermal loading and the difficulty to take it into account at design level. The objective of this report is to study the initiation and the propagation of crack under thermal loading. In this aim the CEA has developed a new experiment named FAT3D. The various experiments carried out showed the harmfulness of a thermal loading, which makes it possible to rapidly initiate a network of cracks and to propagate one (or some) cracks through the totally thickness of the component under certain conditions. These experimental results associated with a mechanical analysis put at fault the usual criteria of damage based on the variations of the equivalent strain. In addition, the study of the propagation stage shows the importance of the plasticity which, in the case of a thermal loading, slows down the propagation of the crack. (author)
Nam, Ki-Woo; Kang, Chang-Yong; Do, Jae-Yoon; Ahn, Seok-Hwan; Lee, Sang-Kee
2001-06-01
The fatigue crack propagation of super duplex stainless steel was investigated for the effect of various volume fractions of the austenite phase by changing the heat treatment temperature. We also analyzed acoustic emission signals obtained during the fatigue crack propagation by the time-frequency analysis method. As the temperature of the heat treatment increased, the volume fraction of austenite decreased and coarse grain was obtained. The specimen treated at 1200 had a longer fatigue life and slower rate of crack growth. Results of time-frequency analysis of acoustic emission signals during the fatigue test showed the main frequency of 200-300 kHz to have no correlation with heat treatment and crack length, and the 500 kHz signal to be due to dimples and separation of inclusion.
Transient dynamic crack propagation in gas pressurised pipelines
International Nuclear Information System (INIS)
Caldis, E.S.; Owen, D.R.J.; Taylor, C.
1983-01-01
The prime limitation of dynamic fracture analysis is the lack of a fundamental crack advance theory which can be easily and economically adopted for use with numerical models. The necessity for the inclusion of inertia effects in the solution of certain problem classes is now evident, but most transient dynamic fracture models considered to date include (of necessity) some intuitive/empirical parameters with a frequent need of a priori knowledge of experimental solutions. The particular problem considered in this study is Mode I transient dynamic crack propagation in gas pressurised pipelines. The steel pipe is modelled using thin shell Semiloof finite elements and its transient response is coupled to a one-dimensional finite element model of the compressible gas equations, incorporating a lateral gas flow parameter. The pipe is governed by the usual dynamic equilibrium equation which is discretised in the time domain by a central difference explicit algorithm. The compressible gas response is modelled by the Continuity and Momentum equations and time discretisation is performed by means of a fully backward difference scheme in time. (orig./GL)
3D multiscale crack propagation using the XFEM applied to a gas turbine blade
Holl, Matthias; Rogge, Timo; Loehnert, Stefan; Wriggers, Peter; Rolfes, Raimund
2014-01-01
This work presents a new multiscale technique to investigate advancing cracks in three dimensional space. This fully adaptive multiscale technique is designed to take into account cracks of different length scales efficiently, by enabling fine scale domains locally in regions of interest, i.e. where stress concentrations and high stress gradients occur. Due to crack propagation, these regions change during the simulation process. Cracks are modeled using the extended finite element method, such that an accurate and powerful numerical tool is achieved. Restricting ourselves to linear elastic fracture mechanics, the -integral yields an accurate solution of the stress intensity factors, and with the criterion of maximum hoop stress, a precise direction of growth. If necessary, the on the finest scale computed crack surface is finally transferred to the corresponding scale. In a final step, the model is applied to a quadrature point of a gas turbine blade, to compute crack growth on the microscale of a real structure.
International Nuclear Information System (INIS)
Kobayashi, S.; Horikiri, M.
2001-06-01
This report shows the results of crack inspection in crack propagation tests that were carried out at the Air-cooling Thermal Transient Test Facility (ATTF). Test specimens were made of 304 type austenitic stainless steel, and they were the same cylindrical shape, 1,500 mm in height, 130 mm in outer diameter and 30 mm in thickness. And they had initial slits machined on inner surfaces. Firstly the specimens were heated up to 650degC in a furnace, then cooled by pressurized air blowing through the specimen for 90 seconds. These cyclic changes of temperature gradients in the wall of specimens were loaded. Specimens were tested for several years. The specimen No. CPTT-102 with machined two circumferential slits and two semi-elliptical slits was tested up to 10,000 cycles. And the specimen No. CPTT-103 with machined six semi-elliptical slits of different length respectively was tested up to 5,000 cycles. Cracks of specimens were inspected nondestructively for a giving cycle in these tests. Applied inspection methods were ultra-sonic testing, potential-drop method and inner surface observation. Ultra-sonic testing was carried out by applying the pulse-echo method. Potential-drop testing was carried out by measurement of localized constant direct current beyond cracks. Photographs of the inner surface of specimens were taken using a bore-scope. The results of ultra-sonic testing have been close to destructive test results. The depth of crack by the potential-drop method was almost corresponding to destructive test results, too. Photographs of the inner surface were synthesized by the computer, and connection between main crack and hair crack was observed. (author)
Crack resistance behaviour of an intermetallic Ti-Al-Si-Nb alloy at room temperature
International Nuclear Information System (INIS)
Wittkowsky, B.U.; Pfuff, M.J.
1996-01-01
The room temperature crack growth behaviour of a Ti-Al-Si-Nb alloy consisting of the two intermetallic phases (Ti, Nb) 3 (Al, Si) and (Ti, Nb) 5 (Si, Al) 3 is investigated in the present paper. The material exhibits a heterogeneous disordered microstructure and fails in a brittle manner. Crack growth is associated with a pronounced crack resistance behaviour. For a sample of nominally identical specimens the R-curves scatter around a mean curve with a standard deviation which remains roughly constant as the crack grows. A natural extension of the bundle model introduced in a previous paper is used to simulate R-curves and their scatter is in reasonably good agreement with the experimental findings. (orig.)
Crack and fracture behaviour in tough ductile materials
International Nuclear Information System (INIS)
Venter, R.D.; Hoeppner, D.W.
1985-10-01
The report describes various approaches and developments pertaining to the understanding of crack and fracture behaviour in tough ductile materials. The fundamental elastic fracture mechanics concepts based on the concepts of energy, stress field, and displacement are introduced and their interrelationships demonstrated. The extension of these concepts to include elasto-plastic fracture mechanics considerations is reviewed in the context of the preferred options available for the development of appropriate design methodologies. The recommendations of the authors are directed towards the continued development of the J-integral concept. This energy-based concept, in its fundamental form, has a sound theoretical basis and as such offers the possibility of incorporating elasto-plastic fracture mechanics considerations in the crack and fracture behaviour of tough ductile materials. It must however be emphasized that the concise defintion of J becomes increasingly suspect as the crack length increases. J is not a material property, as is J IC , but emerges as a useful empirical parameter which is dependent upon the particular geometry and the loading imposed on the structure. It is proposed that 'lowest bound' J-resistance curves and the associated J-T curves be experimentally developed and employed in the design process. Improvements to these 'lowest bounds' can be developed through extensive analysis of the twin J-CTOA criteria and validation of this approach through near full scale tests
Initiation and propagation of rebar corrosion in carbonated and cracked concrete
International Nuclear Information System (INIS)
Ghantous, Rita-Maria
2016-01-01
This thesis aims to study the carbonation-induced corrosion initiation and propagation in cracked concrete under different conditions. It is performed in the framework of concrete ageing management of cooling towers of Electricity of France (EDF) nuclear power plants. Indeed some of them can be affected by cracks which may promote the carbonation of the concrete surrounding the cracks and induce a rapid reinforcement corrosion initiation in the carbonated area. Firstly, cracks representative of those encountered in the cooling towers concrete are reproduced on laboratory specimens using the three point bending test. Three crack openings are obtained (100 μm, 300 μm and 500 μm). Cracked specimens are thereafter exposed to accelerated carbonation for two aims. First for the acceleration of the concrete neutralization phase which ensure the suitable thermodynamic conditions for active corrosion initiation. Second, for the estimation of the length of the mechanically damaged steel/binder interface supposed to be comparable to the carbonated length along the rebar on both sides of the crack. It is found that carbonation at 50% CO_2 is not suitable here because it overestimated the damaged zone length, maybe due to enhanced carbonation shrinkage. The second part aims to investigate the corrosion initiation and propagation phases while varying several parameters. For this purpose, cracked and carbonated specimens are subjected to corrosion under different exposure conditions. Specimens showing different crack widths and different types of binder are corroded in a reference test in which 30 minutes of rain occurs each 3 days at 20 C. Additionally, some corrosion tests are realized under raining/drying cycles for 3 minutes rain, other at 40 C and other in natural environmental conditions. Moreover, some cracked specimens are exposed in different orientations with respect to rain. Furthermore, specimens with different bars locations are prepared in order to investigate
DEFF Research Database (Denmark)
Hodgdon, Jennifer A.; Sethna, James P.
1993-01-01
We derive a general crack-propagation law for slow brittle cracking, in two and three dimensions, using discrete symmetries, gauge invariance, and gradient expansions. Our derivation provides explicit justification for the ‘‘principle of local symmetry,’’ which has been used extensively to describe...
Dislocation arrangement in the plastic zone for propagating cracks in nickel
International Nuclear Information System (INIS)
Kobayashi, S.; Ohr, S.M.
1985-01-01
Since nickel is a metal of high stacking fault energy, it is of interest to study the arrangement of dislocations in the plastic zone for propagating cracks and to compare the results with those found in metals of low stacking fault energy. It has been found that two distinct distributions of dislocations in the plastic zone are associated with cracks in nickel. In one of these, the plastic zone appeared as a thin ribbon and consisted of a number of partial dislocations with stacking fault fringes. From contrast analysis and stereoscopic observations, the crack was found to be approximately mode III type, and the plane of the plastic zone was identified as (111). The crack geometry was very similar to that observed in metals of low stacking fault energy, namely, stainless steel and copper. The second type of plastic zone observed was not in the form of a thin ribbon; that is, the dislocations in the plastic zone were not split into partial dislocations. Since the dislocations were not split, they cross-slipped readily from the original slip plane and formed a broad plastic zone
Lu, Mingyu; Qu, Yongwei; Lu, Ye; Ye, Lin; Zhou, Limin; Su, Zhongqing
2012-04-01
An experimental study is reported in this paper demonstrating monitoring of surface-fatigue crack propagation in a welded steel angle structure using Lamb waves generated by an active piezoceramic transducer (PZT) network which was freely surface-mounted for each PZT transducer to serve as either actuator or sensor. The fatigue crack was initiated and propagated in welding zone of a steel angle structure by three-point bending fatigue tests. Instead of directly comparing changes between a series of specific signal segments such as S0 and A0 wave modes scattered from fatigue crack tips, a variety of signal statistical parameters representing five different structural status obtained from marginal spectrum in Hilbert-huang transform (HHT), indicating energy progressive distribution along time period in the frequency domain including all wave modes of one wave signal were employed to classify and distinguish different structural conditions due to fatigue crack initiation and propagation with the combination of using principal component analysis (PCA). Results show that PCA based on marginal spectrum is effective and sensitive for monitoring the growth of fatigue crack although the received signals are extremely complicated due to wave scattered from weld, multi-boundaries, notch and fatigue crack. More importantly, this method indicates good potential for identification of integrity status of complicated structures which cause uncertain wave patterns and ambiguous sensor network arrangement.
DEFF Research Database (Denmark)
Jacobsen, Hjalte Sylvest; Puig-Molina, A.; Dalskov, N.
2016-01-01
sintering of the rejected tabletized support material are studied by 3D X-ray tomography. This is a powerful technique, which due to its nondestructive nature is suitable to study the development of internal cracks in the tablets during sintering. Cracks could be identified in the green tablet (before...... properly, cracks may arise and propagate during the sintering of the tablets. This can lead to weak sintered tablets that get rejected in the quality control. For this work, crack-containing samples of rejected tabletized support were provided. The formation, growth and closure of internal cracks during...
Chudnovsky, A.
1987-01-01
A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.
Lee, H. S.
2018-03-01
Corrosion fatigue crack propagation test was conducted of giga-grade steel and its heat affected zone in pH buffer solutions, and the results were compared with model predictions. Pure corrosion effect on fatigue crack propagation, particularly, in corrosive environment was evaluated by means of the modified Forman equation. As shown in results, the average corrosion rate determined from the ratio of pure corrosion induced crack length to entire crack length under a cycle load were 0.11 and 0.37 for base metal and heat affected zone, respectively, with load ratio of 0.5, frequency of 0.5 and pH 10.0 environment. These results demonstrate new interpretation methodology for corrosion fatigue crack propagation enabling the pure corrosion effects on the behavior to be determined.
Delrue, Steven; Aleshin, Vladislav; Truyaert, Kevin; Bou Matar, Olivier; Van Den Abeele, Koen
2018-01-01
Our study aims at the creation of a numerical toolbox that describes wave propagation in samples containing internal contacts (e.g. cracks, delaminations, debondings, imperfect intergranular joints) of known geometry with postulated contact interaction laws including friction. The code consists of two entities: the contact model and the solid mechanics module. Part I of the paper concerns an in-depth description of a constitutive model for realistic contacts or cracks that takes into account the roughness of the contact faces and the associated effects of friction and hysteresis. In the crack model, three different contact states can be recognized: contact loss, total sliding and partial slip. Normal (clapping) interactions between the crack faces are implemented using a quadratic stress-displacement relation, whereas tangential (friction) interactions were introduced using the Coulomb friction law for the total sliding case, and the Method of Memory Diagrams (MMD) in case of partial slip. In the present part of the paper, we integrate the developed crack model into finite element software in order to simulate elastic wave propagation in a solid material containing internal contacts or cracks. We therefore implemented the comprehensive crack model in MATLAB® and introduced it in the Structural Mechanics Module of COMSOL Multiphysics®. The potential of the approach for ultrasound based inspection of solids with cracks showing acoustic nonlinearity is demonstrated by means of an example of shear wave propagation in an aluminum sample containing a single crack with rough surfaces and friction. Copyright © 2017 Elsevier B.V. All rights reserved.
Influence of nano-inclusions' grain boundaries on crack propagation modes in materials
International Nuclear Information System (INIS)
Karakasidis, T.E.; Charitidis, C.A.
2011-01-01
The effect of nano-inclusions on materials' strength and toughness has attracted great interest in recent years. It has been shown that tuning the morphological and microstructural features of materials can tailor their fracture modes. The existence of a characteristic size of inclusions that favours the fracture mode (i.e. transgranular or intergranular) has been experimentally observed but also predicted by a 2D model based on energetic arguments which relates the crack propagation mode to the ratio of the interface area between the crystalline inclusion and the matrix with the area of the crystallite inclusion in a previous work. In the present work, a 3D model is proposed in order to extend the 2D model and take into account the influence of the size of grain boundary zone on the toughening/hardening behavior of the material as it was observed experimentally in the literature. The model relates crack propagation mode to the ratio of the volume of the grain boundary zone between the crystalline inclusion and the matrix with the volume of the nano-inclusion. For a ratio below a critical value, transgranular propagation is favoured while for larger values, intergranular propagation is favoured. We also demonstrate that the extent of the grain boundary region also can significantly affect this critical value. The results of the model are in agreement with the literature experimental observations related to the toughening/hardening behavior as a function of the size of crystalline inclusions as well as the width of the grain boundary regions.
Mode I and mixed I/III crack initiation and propagation behavior of V-4Cr-4Ti alloy at 25{degrees}C
Energy Technology Data Exchange (ETDEWEB)
Li, H.X.; Kurtz, R.J.; Jones, R.H. [Pacific Northwest National Lab., Richland, WA (United States)
1997-04-01
The mode I and mixed-mode I/III fracture behavior of the production-scale heat (No. 832665) of V-4Cr-4Ti has been investigated at 25{degrees}C using compact tension (CT) specimens for a mode I crack and modified CT specimens for a mixed-mode I/III crack. The mode III to mode I load ratio was 0.47. Test specimens were vacuum annealed at 1000{degrees}C for 1 h after final machining. Both mode I and mixed-mode I/III specimens were fatigue cracked prior to J-integral testing. It was noticed that the mixed-mode I/III crack angle decreased from an initial 25 degrees to approximately 23 degrees due to crack plane rotation during fatigue cracking. No crack plane rotation occurred in the mode I specimen. The crack initiation and propagation behavior was evaluated by generating J-R curves. Due to the high ductility of this alloy and the limited specimen thickness (6.35 mm), plane strain requirements were not met so valid critical J-integral values were not obtained. However, it was found that the crack initiation and propagation behavior was significantly different between the mode I and the mixed-mode I/III specimens. In the mode I specimen crack initiation did not occur, only extensive crack tip blunting due to plastic deformation. During J-integral testing the mixed-mode crack rotated to an increased crack angle (in contrast to fatigue precracking) by crack blunting. When the crack initiated, the crack angle was about 30 degrees. After crack initiation the crack plane remained at 30 degrees until the test was completed. Mixed-mode crack initiation was difficult, but propagation was easy. The fracture surface of the mixed-mode specimen was characterized by microvoid coalescence.
Energy Technology Data Exchange (ETDEWEB)
Bongue Boma, M
2007-12-15
We propose a model describing the evolution of mechanical and permeability properties of concrete under slow mechanical loading. Calling upon the theory of continua with microstructure, the kinematic of the domain is enriched by a variable characterising size and orientation of the crack field. We call upon configurational forces to deal with crack propagation and we determine the balance equations governing both strain and propagation. The geometry of the microstructure is representative of the porous media: the permeability is obtained from the resolution of Stokes equations in an elementary volume. An example has been treated: we considered simple assumptions (uniform crack field, application of linear fracture mechanics...) and we determined the behaviour of a body under tensile loading. Strain, crack propagation and stiffness loss are completely assessed. Finally the evolution of permeability is plotted: once activated, crack propagation is the main cause of water tightness loss. (author)
Cracked rotors. A survey on static and dynamic behaviour including modelling and diagnosis
Energy Technology Data Exchange (ETDEWEB)
Bachschmid, Nicolo; Pennacchi, Paolo; Tanzi, Ezio [Politecnico di Milano (Italy). Dept. of Mechanical Engineering
2010-07-01
Cracks can develop in rotating shafts and can propagate to relevant depths without affecting consistently the normal operating conditions of the shaft. In order to avoid catastrophic failures, accurate vibration analyses have to be performed for crack detection. The identification of the crack location and depth is possible by means of a model based diagnostic approach, provided that the model of the crack and the model of the cracked shaft dynamical behavior are accurate and reliable. This monograph shows the typical dynamical behavior of cracked shafts and presents tests for detecting cracks. The book describes how to model cracks, how to simulate the dynamical behavior of cracked shaft, and compares the corresponding numerical with experimental results. All effects of cracks on the vibrations of rotating shafts are analyzed, and some results of a numerical sensitivity analysis of the vibrations to the presence and severity of the crack are shown. Finally the book describes some crack identification procedures and shows some results in model based crack identification in position and depth. The book is useful for higher university courses in mechanical and energetic engineering, but also for skilled technical people employed in power generation industries. (orig.)
International Nuclear Information System (INIS)
Shin, Jeong Woo; Lee, Young Shin
2011-01-01
The dynamic propagation of an interface crack between two functionally graded material (FGM) layers under anti-plane shear is analyzed using the integral transform method. The properties of the FGM layers vary continuously along their thicknesses. The properties of the two FGM layers vary and the two layers are connected weak-discontinuously. A constant velocity Yoffe-type moving crack is considered. The Fourier transform is used to reduce the problem to a dual integral equation, which is then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGM to show the effect of the gradient of material properties, crack moving velocity, and thickness of FGM layers. The following are helpful to increase resistance to interface crack propagation in FGMs: a) increasing the gradient of material properties, b) an increase of shear modulus and density from the interface to the upper and lower free surface, and c) increasing the thickness of the FGM layer. The DERR increases or decreases with increase of the crack moving velocity
Energy Technology Data Exchange (ETDEWEB)
Bongue Boma, M
2007-12-15
We propose a model describing the evolution of mechanical and permeability properties of concrete under slow mechanical loading. Calling upon the theory of continua with microstructure, the kinematic of the domain is enriched by a variable characterising size and orientation of the crack field. We call upon configurational forces to deal with crack propagation and we determine the balance equations governing both strain and propagation. The geometry of the microstructure is representative of the porous media: the permeability is obtained from the resolution of Stokes equations in an elementary volume. An example has been treated: we considered simple assumptions (uniform crack field, application of linear fracture mechanics...) and we determined the behaviour of a body under tensile loading. Strain, crack propagation and stiffness loss are completely assessed. Finally the evolution of permeability is plotted: once activated, crack propagation is the main cause of water tightness loss. (author)
Crack propagation from a filled flaw in rocks considering the infill influences
Chang, Xu; Deng, Yan; Li, Zhenhua; Wang, Shuren; Tang, C. A.
2018-05-01
This study presents a numerical and experimental study of the cracking behaviour of rock specimen containing a single filled flaw under compression. The primary aim is to investigate the influences of infill on crack patterns, load-displacement response and specimen strength. The numerical code RFPA2D (Rock Failure Process Analysis) featured by the capability of modeling heterogeneous materials is employed to develop the numerical model, which is further calibrated by physical tests. The results indicate that there exists a critical infill strength which controls crack patterns for a given flaw inclination angle. For case of infill strength lower than the critical value, the secondary or anti-cracks are disappeared by increasing the infill strength. If the infill strength is greater than the critical value, the filled flaw has little influence on the cracking path and the specimen fails by an inclined crack, as if there is no flaw. The load-displacement responses show specimen stiffness increases by increasing infill strength until the infill strength reaches its critical value. The specimen strength increases by increasing the infill strength and almost keeps constant as the infill strength exceeds its critical value.
Effect of overloads on fatigue crack propagation rate
International Nuclear Information System (INIS)
Kogaev, V.P.; Bojtsov, B.V.; Petukhov, Yu.V
1986-01-01
An overload coefficient Q, the number of overload cycles Nsub(0), the value of the stress intensity coefficient swing of basic loading conditions ΔK are experimentally studied for their effect on the delay of the fatigue crack propagation Nsub(D) in 30KhGSNA steel. Results of the study are presented. It is shown that as a result of single overloads the value attains 60 - 10 thous. cycles. The delay Nsub(D) grows with the overload coefficient Q=Ksub(max)sup(0)/Ksub(max) and the number of the overload cycles Nsub(0). The regularity indicated is described by the equations valid within the limits of variation in Q and Nsub(0) values studied in the paper
International Nuclear Information System (INIS)
Uematsu, Y.; Tokaji, K.; Horie, T.; Nishigaki, K.
2007-01-01
Fracture toughness and fatigue crack propagation (FCP) have been studied using compact tension (CT) specimens of as-cast and subzero-treated materials in a cast iron with spheroidal vanadium carbides (VCs) dispersed in the martensitic matrix microstructure. X-ray diffraction (XRD) analysis revealed that retained austenite was transformed to martensite by subzero treatment. Vickers hardness was increased from 738 for the as-cast material to 782 for the subzero-treated material, which could be attributed to retained austenite to martensite transformation. The subzero-treated material exhibited lower fracture toughness than the as-cast material because soft and ductile retained austenite which possesses high fracture toughness was transformed to martensite in the subzero-treated material. Intrinsic FCP resistance after taking account of crack closure was decreased by the subzero treatment, which was attributed to the predominant crack propagation through the interface between VCs and the matrix and the straight crack path in the matrix microstructure
Effect of a cracked surface of porous silicon on the behaviour of the acoustic signature
Directory of Open Access Journals (Sweden)
Bouhedja Samia
2014-06-01
Full Text Available We study in this work the effect of a crack, located on the porous silicon, Psi, surface on the propagation of Rayleigh waves. We simulate and analyse the acoustic signature V(z according porosity at 142 MHz, to study the microstructure of PSi around the crack.
Numerical analysis of the influence of liquid on propagation of a rolling contact fatigue crack
Directory of Open Access Journals (Sweden)
M. Olzak
2017-10-01
Full Text Available Numerical investigations of the propagation of rolling contact fatigue crack filled by the liquid have been conducted. Two models of fluid crack interaction have been considered. In the first model called 䖓hydrostatic� the assumption of incompressible, inviscid and weightless liquid was accepted. It was also assumed that due to the wheel load the trapped liquid could not get outside the crack and its volume remained constant until the rising pressure would open up the crack mouth again. On this assumption the analysis has a steady-state character. In the second model it has been assumed that the crack is filled by the viscous, incompressible fluid and the fluid motion as well as the resulting pressure distribution can be represented by one-dimensional form of the Reynolds equation. The method for solving the problem of the coupled motion of liquid and crack faces has been developed and series of calculation were made. The method has been employed for the predicting of crack deformation in the course of wheel rolling
Steady State Crack Propagation in Layered Material Systems Displaying Visco-plastic Behaviour
DEFF Research Database (Denmark)
Nielsen, Kim Lau
2012-01-01
The steady state fracture toughness of elastic visco-plastic materials is studied numerically, using both a conventional and a higher order model. Focus is on the combined effect of strain hardening, strain gradient hardening and strain rate hardening on cracking in layered material systems...
Elastic-plastic analysis of local and integral straining behaviour in a cracked plate
International Nuclear Information System (INIS)
Grueter, L.; Ruettenauer, B.
1982-01-01
For components of the primary coolant system of the German LMFBR prototype reactor SNR-300, integrity against anticipated accidents (Bethe-Tait) has to be shown for a cracked structure. Within this programme a number of tests with cracked wide plate specimens yielding overall limit strains of approximately 15% have been run; finite element calculations have been infinated for the wide plate geometry. The paper discusses the straining behaviour of a cracked plate by considering the numerical simulation of structures strained up to such high levels. The stress-strain diagram of the weldment of the austenitic stainless steel X6 CrNi 18 at 450 0 C has been used. Plane strain and stress conditions have been prescribed. The original plate dimensions (t = thickness = 40 mm; h = height = 400 mm) have been used as well as a similar, but smaller plate of t = 8.8 mm width. The crack length is defined as 0.1 t. The results show that for a cracked plate under high plastic strain the near-crack-tip-field values still govern the structural mechanical behaviour. Concerning the absolute dimensions the effects known for elasticity retain their influence in the plastic regime; however, the crack location becomes more unimportant with increasing strain, i.e. the appropriate pure geometry factor tends to unity in the plastic regime. The center-crack, defined as 2a = 0.1 t, corresponds to an equivalent edge crack of depth a = 0.05 t in the elastic case. It can be shown that for high plastic strains this correspondence remains fully valid. (orig.)
Effect of residual stress in layered ceramic microcomposites on crack propagation during fracture
International Nuclear Information System (INIS)
Tomaszewski, H.; Strzeszewski, J.; Gebicki, W.
1998-01-01
Laminar composites, containing layers of Y-ZrO 2 and either Al 2 O 3 or a mixture of Al 2 O 3 and ZrO 2 have been fabricated using a sequential centrifuging technique of water solutions containing of suspended particles. Controlled crack growth experiments with notched beams of composites were done and showed the significant effect of barrier layer thickness and composition of the crack propagation path during fracture. Distinct crack deflection in alumina layers was observed. The increase of crack deflection angle with the alumina layer thickness was also found. In the case of the barrier layer made of mixture, crack deflection did not occur independently on layer thickness. The observed changes have been correlated with the radial distribution of residual stresses in barrier layers created during cooling of sintered composites from fabrication temperature. The stress found were the result of the differences in the thermal expansion and sintering shrinkage of alumina and zirconia and the crystallographically anisotropic thermal expansion of the alumina. The residual stress distribution has been measured by piezo-spectroscopy based on the optical fluorescence of Cr + dopants in alumina. (author)
Energy Technology Data Exchange (ETDEWEB)
Nagano, K [Muroran Institute of Technology, Hokkaido (Japan)
1997-10-22
A study has been performed on underground cracks working as a geothermy reservoir layer, with respect to characteristics of elastic waves propagating with their energy concentrated on a boundary between rocks around the cracks and fluid in the underground cracks, or `crack waves`. The study has modeled a multi-crack reservoir layer according to the three-layer structure of the fluid layer and low-velocity solid layers around the former layer, whereas crack waves propagating therein were discussed for their dispersion characteristics. As a result of discussions, a guideline to the crack wave measurement at actual fields was put together as follows: because the low-velocity layer affects the dispersion characteristics of the crack waves, the structure and characteristics of the multi-crack reservoir layer may possibly be evaluated by measuring the velocity of the crack waves; evaluating the low-velocity layers requires proper selection of frequency of the crack wave to be measured; for example, at the Higashi Hachimantai field, a crack wave of several hundred hertz must be analyzed; and thickness of the low-velocity layers around main cracks, which can be estimated from the velocity of the crack wave is two meters at the greatest. 6 refs., 3 figs., 2 tabs.
Fatigue crack paths under the influence of changes in stiffness
Directory of Open Access Journals (Sweden)
G. Kullmer
2016-02-01
Full Text Available An important topic of the Collaborative Research Centre TRR 30 of the Deutsche Forschungsgemeinschaft (DFG is the crack growth behaviour in graded materials. In addition, the growth of cracks in the neighbourhood of regions and through regions with different material properties belongs under this topic. Due to the different material properties, regions with differing stiffness compared to the base material may arise. Regions with differing stiffness also arise from ribs, grooves or boreholes. Since secure findings on the propagation behaviour of fatigue cracks are essential for the evaluation of the safety of components and structures, the growth of cracks near changes in stiffness has to be considered, too. Depending on the way a crack penetrates the zone of influence of such a change in stiffness and depending on whether this region is more compliant or stiffer than the surrounding area the crack may grow towards or away from this region. Both cases result in curved crack paths that cannot be explained only by the global loading situation. To evaluate the influence of regions with differing stiffness on the path of fatigue cracks the paths and the stress intensity factors of cracks growing near and through regions with differing stiffness are numerically determined with the program system ADAPCRACK3D. Therefore, arrangements of changes in stiffness modelled as material inclusions with stiffness properties different from the base material or modelled as ribs and grooves are systematically varied to develop basic conclusions about the crack growth behaviour near and through changes in stiffness.
International Nuclear Information System (INIS)
Raquet, O.
1994-01-01
A purely phenomenological study of stress corrosion cracking was performed using the couple Z2CN 18.10 (304L) austenitic stainless steel/boiling MgCl 2 aqueous solution. The exploitation of the morphological information (shape of the cracks and size distribution) available after constant elongation rate tests led to the proposal of an analytical expression of the crack initiation and growth rates. This representation allowed to quantitatively characterize the influence of the applied strain rate as well as the effect of corrosion inhibitors on the crack initiation and propagation phases. It can be used in the search for the stress corrosion cracking mechanisms as a 'riddle' for the determination of the rate controlling steps. As a matter of fact, no mechanistic hypothesis has been used for its development. (author)
Hydride effect on crack instability of Zircaloy cladding
Energy Technology Data Exchange (ETDEWEB)
Tseng, Che-Chung, E-mail: cctseng@iner.gov.tw [Institute of Nuclear Energy Research, No. 1000, Wunhua Road, Jiaan Village, Lungtan, Township, Taoyuan County 32546, Taiwan (China); Sun, Ming-Hung [Institute of Nuclear Energy Research, No. 1000, Wunhua Road, Jiaan Village, Lungtan, Township, Taoyuan County 32546, Taiwan (China); Chao, Ching-Kong [Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 106, Taiwan (China)
2014-04-01
Highlights: • Radial hydrides near the crack tip had a significant effect on crack propagation. • For radial hydrides off the crack line vertically, the effect on crack propagation was notably reduced. • The longer hydride platelet resulted in a remarkable effect on crack propagation. • A long split in the radial hydride precipitate would enhance crack propagation. • The presence of circumferential hydride among radial hydrides may play an important role in crack propagation. - Abstract: A methodology was proposed to investigate the effect of hydride on the crack propagation in fuel cladding. The analysis was modeled based on an outside-in crack with radial hydrides located near its crack tip. The finite element method was used in the calculation; both stress intensity factor K{sub I} and J integral were applied to evaluate the crack stability. The parameters employed in the analysis included the location of radial hydride, hydride dimensions, number of hydrides, and the presence of circumferential hydride, etc. According to our study, the effective distance between a radial hydride and the assumed cladding surface crack for the enhancement of crack propagation proved to be no greater than 0.06 mm. For a hydride not on the crack line, it would induce a relatively minor effect on crack propagation if the vertical distance was beyond 0.05 mm. However, a longer hydride precipitate as well as double radial hydrides could have a remarkable effect on crack propagation. A combined effect of radial and circumferential hydrides was also discussed.
Modeling time-dependent corrosion fatigue crack propagation in 7000 series aluminum alloys
Mason, Mark E.; Gangloff, Richard P.
1994-01-01
Stress corrosion cracking and corrosion fatigue experiments were conducted with the susceptible S-L orientation of AA7075-T651, immersed in acidified and inhibited NaCl solution, to provide a basis for incorporating environmental effects into fatigue crack propagation life prediction codes such as NASA FLAGRO. This environment enhances da/dN by five to ten-fold compared to fatigue in moist air. Time-based crack growth rates from quasi-static load experiments are an order of magnitude too small for accurate linear superposition prediction of da/dN for loading frequencies above 0.001 Hz. Alternate methods of establishing da/dt, based on rising-load or ripple-load-enhanced crack tip strain rate, do not increase da/dt and do not improve linear superposition. Corrosion fatigue is characterized by two regimes of frequency dependence; da/dN is proportional to f(exp -1) below 0.001 Hz and to F(exp 0) to F(exp -0.1) for higher frequencies. Da/dN increases mildly both with increasing hold-time at K(sub max) and with increasing rise-time for a range of loading waveforms. The mild time-dependence is due to cycle-time-dependent corrosion fatigue growth. This behavior is identical for S-L nd L-T crack orientations. The frequency response of environmental fatigue in several 7000 series alloys is variable and depends on undefined compositional or microstructural variables. Speculative explanations are based on the effect of Mg on occluded crack chemistry and embritting hydrogen uptake, or on variable hydrogen diffusion in the crack tip process zone. Cracking in the 7075/NaCl system is adequately described for life prediction by linear superposition for prolonged load-cycle periods, and by a time-dependent upper bound relationship between da/dN and delta K for moderate loading times.
Effect of cold rolling on fatigue crack propagation of TiNi/A16061 shape memory composite
International Nuclear Information System (INIS)
Lee, Jin Kyung; Lee, Sang Pill; Park, Young Chul; Lee, Kyu Chang; Cho, Youn Ho; Lee, Joon Hyun
2005-01-01
TiNi alloy fiber was used to recover the original shape of materials using its shape memory effect. The shape memory alloy plays an important role within the metal matrix composite. The shape memory alloy can control the crack propagation in metal matrix composite, and improve the tensile strength of the composite. In this study, TiNi/A16061 Shape Memory Alloy(SMA) composite was fabricated by hot press method, and pressed by a roller for its strength improvement. The four kinds of specimens were fabricated with 0%, 3.2%, 5.2% and 7% volume fraction of TiNi alloy fiber, respectively. A fatigue test has performed to evaluate the crack initiation and propagation for the TiNi/A16061 SMA composite fabricated by this method. In order to study the shape memory effect of the TiNi alloy fiber, the test has also done under both conditions of the room temperature and high temperature. The relationship between the crack growth rate and the stress intensity factor was clarified for the composite, and the cold rolling effect was also studied
Energy Technology Data Exchange (ETDEWEB)
Wu, Huan Chun; Yang, Bin [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing (China); Chen, Yue Feng; Chen, Xu Dong [Collaborative Innovation Center of Steel Technology, Beijing (China)
2017-06-15
The fatigue crack propagation behaviors of Z3CN20.09M duplex stainless steel (DSS) were investigated by studying oxide films of specimens tested in 290°C water and air. The results indicate that a full oxide film that consisted of oxides and hydroxides was formed in 290°C water. By contrast, only a half-baked oxide film consisting of oxides was formed in 290°C air. Both environments are able to deteriorate the elastic modulus and hardness of the oxide films, especially the 290°C water. The fatigue lives of the specimens tested in 290°C air were about twice of those tested in 290°C water at all strain amplitudes. Moreover, the crack propagation rates of the specimen tested in 290°C water were confirmed to be faster than those tested in 290°C air, which was thought to be due to the deteriorative strength of the oxide films induced by the mutual promotion of oxidation and crack propagation at the crack tip. It is noteworthy that the crack propagation can be postponed by the ferrite phase in the DSS, especially when the specimens were tested in 290°C water.
Directory of Open Access Journals (Sweden)
Leyong Chen
2015-12-01
Full Text Available The fissures and rock bridges with different dips had different contributions to crack's initiation, propagation, convergence and penetration. In this paper, based on the rock fracture theory, the crack's propagation and evolution process on rock specimen with double fissures under uniaxial compression was simulated. As a result, the crack propagation and evolution law of rocks with different fissure dips (α = 0°, 15°, 30°, 45°, 60°, 75°, 90°; β = 45° and different rock bridge dips (β = 0°, 30°, 45°, 60°, 90°; α = 45° was obtained by numerical tests. Meanwhile, the fissure and rock bridge dips influence on the macro mechanical properties of rock was analyzed. Besides, the paper investigated the influences of different fissure dips and different rock bridge dips on the bridge transfixion. The study is of great significance to reveal the impact of different dips on the mechanical mechanism of multiple-fissures rock under specific conditions, and it also has important theoretical significance for the research on multiple-fissure rock.
Propagation of cracks by stress corrosion in conditions of BWR type reactor
International Nuclear Information System (INIS)
Merino C, F.J.; Fuentes C, P.
2004-01-01
In this work, the obtained results when applying the Hydrogen Chemistry to a test tube type Compact Tension (CT), built in austenitic stainless steel 304l, simulating the conditions to those that it operates a Boiling Water Reactor (BWR), temperature 288 C and pressure of 8 MPa are presented. With the application of this water chemistry, seeks to be proven the diminution of the crack propagation speed. (Author)
Energy Technology Data Exchange (ETDEWEB)
Van Brutzel, L
2000-07-01
The aim of this thesis was to understand the mechanism which occurs during the crack at the atomic scale in amorphous silica. The difficulties of the experimental observations at this length scale lead us to use numerical studies by molecular dynamics to access to the dynamical and the thermodynamical informations. We have carried out large simulations with 500000 atoms and studied the structure of the amorphous silica before to studying their behaviours under an imposed strain. The structure of this simulated amorphous silica settled in three length scales. In small length scale between 0 and 5 angstrom glass is composed of tetrahedra, this is close to the crystalline structure. In intermediate length scale between 3 and 10 angstrom tetrahedra are connected together and build rings of different sizes composed in majority between 5 and 7 tetrahedra. In bigger length scale between 15 and 60 angstrom, areas with high density of rings are surrounded by areas with low density of rings. These structural considerations play an important role in initiation and propagation of a crack. Indeed. in this length scale. crack propagates by growth and coalescence of some small cavities which appear in area with low density of rings behind the crack tip. The cavities dissipate the stress with carries away a delay to propagation of the crack. This phenomenons seems ductile and leads to non linear elastic behaviour near the crack tip. We have also shown that the addition of alkali in the amorphous silica changes the structure by creation of nano-porosities and leads to enhance the ductility during the crack propagation. (author)
Assessment of damage localization based on spatial filters using numerical crack propagation models
International Nuclear Information System (INIS)
Deraemaeker, Arnaud
2011-01-01
This paper is concerned with vibration based structural health monitoring with a focus on non-model based damage localization. The type of damage investigated is cracking of concrete structures due to the loss of prestress. In previous works, an automated method based on spatial filtering techniques applied to large dynamic strain sensor networks has been proposed and tested using data from numerical simulations. In the simulations, simplified representations of cracks (such as a reduced Young's modulus) have been used. While this gives the general trend for global properties such as eigen frequencies, the change of more local features, such as strains, is not adequately represented. Instead, crack propagation models should be used. In this study, a first attempt is made in this direction for concrete structures (quasi brittle material with softening laws) using crack-band models implemented in the commercial software DIANA. The strategy consists in performing a non-linear computation which leads to cracking of the concrete, followed by a dynamic analysis. The dynamic response is then used as the input to the previously designed damage localization system in order to assess its performances. The approach is illustrated on a simply supported beam modeled with 2D plane stress elements.
Energy Technology Data Exchange (ETDEWEB)
Suresh, S.; Ritchie, R. O.
1981-11-01
The role of hydrogen gas in influencing fatigue crack propagation is examined for several classes of lower strength pressure vessel and piping steels. Based on measurements over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, crack propagation rates are found to be significantly higher in dehumidified gaseous hydrogen compared to moist air in two distinct regimes of crack growth, namely (i) at the intermediate range of growth typically above approx. 10/sup -5/ mm/cycle, and (ii) at the near-threshold region below approx. 10/sup -6/ mm/cycle approaching lattice dimensions per cycle. Both effects are seen at maximum stress intensities (K/sub max/) far below the sustained-load threshold stress intensity for hydrogen-assisted cracking (K/sub Iscc/). Characteristics of environmentally influenced fatigue crack growth in each regime are shown to be markedly different with regard to fractography and the effect of such variables as load ratio and frequency. It is concluded that the primary mechanisms responsible for the influence of the environment in each regime are distinctly different. Whereas corrosion fatigue behavior at intermediate growth rates can be attributed to hydrogen embrittlement processes, the primary role of moist environments at near-threshold levels is shown to involve a contribution from enhanced crack closure due to the formation of crack surface corrosion deposits at low load ratios.
Liu, Peng; Ju, Yang; Gao, Feng; Ranjith, Pathegama G.; Zhang, Qianbing
2018-03-01
Understanding and characterization of the three-dimensional (3-D) propagation and distribution of hydrofracturing cracks in heterogeneous rock are key for enhancing the stimulation of low-permeability petroleum reservoirs. In this study, we investigated the propagation and distribution characteristics of hydrofracturing cracks, by conducting true triaxial hydrofracturing tests and computed tomography on artificial heterogeneous rock specimens. Silica sand, Portland cement, and aedelforsite were mixed to create artificial heterogeneous rock specimens using the data of mineral compositions, coarse gravel distribution, and mechanical properties that were measured from the natural heterogeneous glutenite cores. To probe the effects of material heterogeneity on hydrofracturing cracks, the artificial homogenous specimens were created using the identical matrix compositions of the heterogeneous rock specimens and then fractured for comparison. The effects of horizontal geostress ratio on the 3-D growth and distribution of cracks during hydrofracturing were examined. A fractal-based method was proposed to characterize the complexity of fractures and the efficiency of hydrofracturing stimulation of heterogeneous media. The material heterogeneity and horizontal geostress ratio were found to significantly influence the 3-D morphology, growth, and distribution of hydrofracturing cracks. A horizontal geostress ratio of 1.7 appears to be the upper limit for the occurrence of multiple cracks, and higher ratios cause a single crack perpendicular to the minimum horizontal geostress component. The fracturing efficiency is associated with not only the fractured volume but also the complexity of the crack network.
Stress Inversion of Coal with a Gas Drilling Borehole and the Law of Crack Propagation
Directory of Open Access Journals (Sweden)
Tianjun Zhang
2017-10-01
Full Text Available For studying the law of crack propagation around a gas drilling borehole, an experimental study about coal with a cavity under uniaxial compression was carried out, with the digital speckle correlation method capturing the images of coal failure. A sequence of coal failure images and the full-field strain of failure were obtained. The strain softening characteristic was shown by the curve. A method of curve dividing—named fitting-damaging—was proposed, combining the least square fitting residual norm and damage fraction. By this method, the five stages and four key points of a stress-strain curve were defined. Then, the full-field stress was inverted by means of the theory of elasticity and the adjacent element weight sharing model. The results show that σci was 30.28–41.71 percent of σf and σcd was 83.08–87.34 percent of σf, calculated by the fitting-damaging method, agreeing with former research. The results of stress inversion showed that under a low stress level (0.15 σf < σ < 0.5 σf, microdamage evolving into plastic failure later was formed around the cavity. Under a high stress level (0.5 σf < σ < 0.85 σf, the region of stress concentration suddenly crazed and formed a brittle crack. When σ ≥ 0.85 σf, the crack was developing, crack lines were connecting with each other, and the coal finally failed. The outcome of the stress inversion was completely concomitant with the images of crack propagation. Additionally, the stress around the cavity was able to be calculated accurately.
Effect of constraint on fatigue crack propagation near threshold in medium carbon steel
Czech Academy of Sciences Publication Activity Database
Hutař, Pavel; Seitl, Stanislav; Knésl, Zdeněk
2006-01-01
Roč. 37, 1-2 (2006), s. 51-57 ISSN 0927-0256 R&D Projects: GA ČR GA101/03/0331; GA ČR GP101/04/P001 Institutional research plan: CEZ:AV0Z20410507 Keywords : Fatigue crack propagation rate * Constraint * Two-parameter fracture mechanics Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.104, year: 2006
International Nuclear Information System (INIS)
Baffie, N.; Stolarz, J.; Magnin, Th.
2000-01-01
The influence of martensitic transformation induced by cyclic straining on the mechanisms of low cycle fatigue damage in a metastable austenitic stainless steel with different grain sizes has been investigated using macroscopic measurements and microscopic observations of short crack evolutions. The amount of martensite formed during cyclic straining increases with increasing plastic strain amplitude and cumulative plastic strain but the dominant parameter is the grain size of austenite. The fine microstructure (D = 10 μm) with maximum martensite fraction of about 20% is characterised by a better fatigue resistance than the coarse one (D 40μm and only 2% of martensite) for the same plastic strain amplitude. Martensitic transformation is found to radically modify the cyclic response of the alloy and consequently the damage mechanisms. Indeed, both short crack nucleation and growth take place exclusively in the transformed regions. A mechanism of short crack propagation based on the γ→ α' transformation assisted by stress concentration at the crack tip is proposed. The indirect influence of grain boundaries in the austenite on crack propagation in the martensite is demonstrated. The better fatigue resistance of metastable alloys with fine granular structure can thus be understood. (authors)
International Nuclear Information System (INIS)
Glasgow, B.B.; Wolfer, W.G.
1986-01-01
Crack growth can result in a breech of a pressure boundary causing coolant loss or in total structural failure. This paper discusses brittle and plastic failure in terms of a unified structural model called the Two Criteria model. The model takes into account the flow stress of the material as well as the fracture toughness. Our results indicate that for fusion reactor first wall structures, ferritic steel is better able to resist crack propagation and subsequent structural failure than 316 stainless steel under the same wall loadings and geometry
International Nuclear Information System (INIS)
Lee, Sang Kee; Nam, Ki Woo; Kang, Chang Yong; Do, Jae Yoon
2000-01-01
On this study, the fatigue crack propagation of super duplex stainless steel is investigated in conditions of various volume fraction of austenite phase by changing heat treatment temperature. And we analysed acoustic emission signals during the fatigue test by time-frequency analysis methods. As the temperature of heat treatment increased, volume fraction of austenite decreased and coarse grain was obtained. The specimen heat treated at 1200 deg. C had longer fatigue life and slower rate of crack growth. As a result of time-frequency analyze of acoustic emission signals during fatigue test, main frequency was 200∼300 kHz having no correlation with heat treatment and crack length, and 500 kHz was obtained by dimple and separate of inclusion
Numerical simulation of ductile-brittle behaviour of cracks in aluminium and bcc iron
International Nuclear Information System (INIS)
Zacharopoulos, Marios
2017-01-01
The principal aim of the present dissertation is to investigate the role of sharp cracks on the mechanical behaviour of crystals under load at the atomic scale. The question of interest is how a pure crystal, which contains a single crack in mechanical equilibrium, deforms. Two metals were considered: aluminium, ductile at any temperature below its melting point, and iron, being transformed from ductile to brittle upon decreasing temperature below T=77 K. Cohesive forces in both metals were modeled via phenomenological n-body potentials. A (010)[001] mode I nano-crack was introduced in the perfect crystalline lattice of each of the studied metals by using appropriate displacements ascribed by anisotropic elasticity. At T=0 K, equilibrium crack configurations were obtained via energy minimization with a mixed type of boundary conditions. Both models revealed that the crack configurations remained stable under a finite range of applied stresses due to the lattice trapping effect. The present thesis proposes a novel approach to interpret the intrinsic mechanical behaviour of the two metallic systems under loading. In particular, the ductile or brittle response of a crystalline system can be determined by examining whether the lattice trapping barrier of a pre-existing crack is sufficient to cause the glide of pre-existing static dislocations on the available slip systems. Simulation results along with experimental data demonstrate that, according to the model proposed, aluminium and iron are ductile and brittle at T=0 K, respectively. (author) [fr
The Reflective Cracking in Flexible Pavements
Directory of Open Access Journals (Sweden)
Pais Jorge
2013-07-01
Full Text Available Reflective cracking is a major concern for engineers facing the problem of road maintenance and rehabilitation. The problem appears due to the presence of cracks in the old pavement layers that propagate into the pavement overlay layer when traffic load passes over the cracks and due to the temperature variation. The stress concentration in the overlay just above the existing cracks is responsible for the appearance and crack propagation throughout the overlay. The analysis of the reflective cracking phenomenon is usually made by numerical modeling simulating the presence of cracks in the existing pavement and the stress concentration in the crack tip is assessed to predict either the cracking propagation rate or the expected fatigue life of the overlay. Numerical modeling to study reflective cracking is made by simulating one crack in the existing pavement and the loading is usually applied considering the shear mode of crack opening. Sometimes the simulation considers the mode I of crack opening, mainly when temperature effects are predominant.
Liu, Heng-Liang; Lin, Chun-Li; Sun, Ming-Tsung; Chang, Yen-Hsiang
2010-06-01
This study investigates micro-crack propagation at the enamel/adhesive interface using finite element (FE) submodeling and element death techniques. A three-dimensional (3D) FE macro-model of the enamel/adhesive/ceramic subjected to shear bond testing was generated and analyzed. A 3D micro-model with interfacial bonding structure was constructed at the upper enamel/adhesive interface where the stress concentration was found from the macro-model results. The morphology of this interfacial bonding structure (i.e., resin tag) was assigned based on resin tag geometry and enamel rod arrangement from a scanning electron microscopy micrograph. The boundary conditions for the micro-model were determined from the macro-model results. A custom iterative code combined with the element death technique was used to calculate the micro-crack propagation. Parallel experiments were performed to validate this FE simulation. The stress concentration within the adhesive occurred mainly at the upper corner near the enamel/adhesive interface and the resin tag base. A simulated fracture path was found at the resin tag base along the enamel/adhesive interface. A morphological observation of the fracture patterns obtained from in vitro testing corresponded with the simulation results. This study shows that the FE submodeling and element death techniques could be used to simulate the 3D micro-stress pattern and the crack propagation noted at the enamel/adhesive interface.
Delayed hydride cracking: alternative pre-cracking method
International Nuclear Information System (INIS)
Mieza, Juan I.; Ponzoni, Lucio M.E.; Vigna, Gustavo L.; Domizzi, Gladys
2009-01-01
The internal components of nuclear reactors built-in Zr alloys are prone to a failure mechanism known as Delayed Hydride Cracking (DHC). This situation has triggered numerous scientific studies in order to measure the crack propagation velocity and the threshold stress intensity factor associated to DHC. Tests are carried out on fatigued pre-crack samples to ensure similar test conditions and comparable results. Due to difficulties in implementing the fatigue pre-crack method it would be desirable to replace it with a pre-crack produced by the same process of DHC, for which is necessary to demonstrate equivalence of this two methods. In this work tests on samples extracted from two Zr-2.5 Nb tubes were conducted. Some of the samples were heat treated to obtain a range in their metallurgical properties as well as different DHC velocities. A comparison between velocities measured in test samples pre-cracked by fatigue and RDIH is done, demonstrating that the pre-cracking method does not affect the measured velocity value. In addition, the incubation (t inc ), which is the time between the application of the load and the first signal of crack propagation, in samples pre-cracked by RDIH, was measured. It was found that these times are sufficiently short, even in the worst cases (lower speed) and similar to the ones of fatigued pre-cracked samples. (author)
Calomino, Anthony Martin
1994-01-01
The subcritical growth of cracks from pre-existing flaws in ceramics can severely affect the structural reliability of a material. The ability to directly observe subcritical crack growth and rigorously analyze its influence on fracture behavior is important for an accurate assessment of material performance. A Mode I fracture specimen and loading method has been developed which permits the observation of stable, subcritical crack extension in monolithic and toughened ceramics. The test specimen and procedure has demonstrated its ability to generate and stably propagate sharp, through-thickness cracks in brittle high modulus materials. Crack growth for an aluminum oxide ceramic was observed to be continuously stable throughout testing. Conversely, the fracture behavior of a silicon nitride ceramic exhibited crack growth as a series of subcritical extensions which are interrupted by dynamic propagation. Dynamic initiation and arrest fracture resistance measurements for the silicon nitride averaged 67 and 48 J/sq m, respectively. The dynamic initiation event was observed to be sudden and explosive. Increments of subcritical crack growth contributed to a 40 percent increase in fracture resistance before dynamic initiation. Subcritical crack growth visibly marked the fracture surface with an increase in surface roughness. Increments of subcritical crack growth loosen ceramic material near the fracture surface and the fracture debris is easily removed by a replication technique. Fracture debris is viewed as evidence that both crack bridging and subsurface microcracking may be some of the mechanisms contributing to the increase in fracture resistance. A Statistical Fracture Mechanics model specifically developed to address subcritical crack growth and fracture reliability is used together with a damaged zone of material at the crack tip to model experimental results. A Monte Carlo simulation of the actual experiments was used to establish a set of modeling input
Study of crack propagation velocity in steel tanks of PWR type reactor
International Nuclear Information System (INIS)
Amzallac, C.; Bernard, J.L.; Slama, G.
1983-05-01
Description and results of a serie of tests carried out on crack propagation velocity of steels in PWR environment (pressurized high temperature water), in order to examine the effects of metallurgical parameters such as chemical composition of steel, especially sulfur and carbon content, and steel type (laminate or forged steels), effects of mechanical parameters such as loading ratio, cycle form, frequency and application mode of loads and of chemical parameters (anodal dissolution or fatigue with hydrogen) [fr
Environmentally assisted cracking behaviour of copper in simulated ground water
International Nuclear Information System (INIS)
Hietanen, S.; Ehrnsten, U.; Saario, T.
1996-05-01
Environmentally assisted cracking (EAC) behaviour of pure oxygen free copper in simulated ground water with additions of sodium nitrite was studied. Low frequency corrosion fatigue tests with high positive load ratio values under crosshead speed control were performed using precracked diskshaped compact specimens C(T). The load ratio values were about 0.9 and the frequencies were between 0.0008 and 0.0017 Hz. Tests were performed under electrochemical potential control in an autoclave at room temperature and at 80 deg C. The aim of the study was to investigate the effects of repository environment on environmentally assisted cracking susceptibility of pure copper. (5 refs., 31 figs., 5 tabs.)
Experimental study of a macrocrack propagation in a concrete specimen subjected to creep loading
Rossi, P.; Boulay, C.; Tailhan, J.-L.; Martin, E.
2013-07-01
Structures managers need a better prediction of the delayed failure of concrete structures, especially for very important structures like nuclear power plant encasement. Sustained loadings at high level (above 75% of loading capacity of the structure), can lead to structure failure after some time. In this study, a series of 4-point bending tests were performed in order to characterize the creep behaviour of pre-cracked beams under high load level. The specimens were made of normal strength concrete. A power law relationship is observed between the secondary deflection creep rate and the failure time. It is also shown that when crack propagation occurs during the creep loading, the creep deflection rate increases with the creep loading level and with the crack propagation rate.
Terahertz non-destructive imaging of cracks and cracking in structures of cement-based materials
Directory of Open Access Journals (Sweden)
Shujie Fan
2017-11-01
Full Text Available Cracks and crack propagation in cement-based materials are key factors leading to failure of structures, affecting safety in construction engineering. This work investigated the application of terahertz (THz non-destructive imaging to inspections on structures of cement-based materials, so as to explore the potential of THz imaging in crack detection. Two kinds of disk specimens made of plain cement mortar and UHMWPE fiber concrete were prepared respectively. A mechanical expansion load device was deployed to generate cracks and control the whole process of cracking. Experimental tests were carried out on cracked specimens by using a commercial THz time domain spectroscopy (THz-TDS during loading. The results show that crack opening and propagation could be examined by THz clearly and the material factors influence the ability of crack resistance significantly. It was found that the THz imaging of crack initiation and propagation agrees with the practical phenomenon and supplies more information about damage of samples. It is demonstrated that the damage behavior of structures of cement-based materials can be successfully detected by THz imaging.
Terahertz non-destructive imaging of cracks and cracking in structures of cement-based materials
Fan, Shujie; Li, Tongchun; Zhou, Jun; Liu, Xiaoqing; Liu, Xiaoming; Qi, Huijun; Mu, Zhiyong
2017-11-01
Cracks and crack propagation in cement-based materials are key factors leading to failure of structures, affecting safety in construction engineering. This work investigated the application of terahertz (THz) non-destructive imaging to inspections on structures of cement-based materials, so as to explore the potential of THz imaging in crack detection. Two kinds of disk specimens made of plain cement mortar and UHMWPE fiber concrete were prepared respectively. A mechanical expansion load device was deployed to generate cracks and control the whole process of cracking. Experimental tests were carried out on cracked specimens by using a commercial THz time domain spectroscopy (THz-TDS) during loading. The results show that crack opening and propagation could be examined by THz clearly and the material factors influence the ability of crack resistance significantly. It was found that the THz imaging of crack initiation and propagation agrees with the practical phenomenon and supplies more information about damage of samples. It is demonstrated that the damage behavior of structures of cement-based materials can be successfully detected by THz imaging.
Crack resistance curve determination of zircaloy-4 cladding
International Nuclear Information System (INIS)
Bertsch, J.; Alam, A.; Zubler, R.
2009-03-01
Fracture mechanics properties of fuel claddings are of relevance with respect to fuel rod integrity. The integrity of a fuel rod, in turn, is important for the fuel performance, for the safe handling of fuel rods, for the prevention of leakages and subsequent dissemination of fuel, for the avoidance of unnecessary dose rates, and for safe operation. Different factors can strongly deteriorate the mechanical fuel rod properties: irradiation damage, thermo-mechanical impact, corrosion or hydrogen uptake. To investigate the mechanical properties of fuel rod claddings which are used in Swiss nuclear power plants, PSI has initiated a program for mechanical testing. A major issue was the interaction between specific loading devices and the tested cladding tube, e.g. in the form of bending or friction. Particular for Zircaloy is the hexagonal closed packed structure of the zirconium crystallographic lattice. This structure implies plastic deformation mechanisms with specific, preferred orientations. Further, the manufacturing procedure of Zircaloy claddings induces a specific texture which plays a salient role with respect to the embrittlement by irradiation or integration of hydrogen in the form of hydrides. Both, the induced microstructure as well as the plastic deformation behaviour play a role for the mechanical properties. At PSI, in a first step inactive thin walled Zircaloy tubes and, for comparison reasons, plates were tested. The validity of the mechanical testing of the non standard tube and plate geometries had to be verified. The used Zircaloy-4 cladding tube sections and small plates of the same wall thickness have been notched, fatigue pre-cracked and tensile tested to evaluate the fracture toughness properties at room temperature, 300 o C and 350 o C. The crack propagation has been determined optically. The test results of the plates have been further used to validate FEM calculations. For each sample a complete crack resistance (J-R) curve could be
Crack resistance curve determination of zircaloy-4 cladding
Energy Technology Data Exchange (ETDEWEB)
Bertsch, J.; Alam, A.; Zubler, R
2009-03-15
Fracture mechanics properties of fuel claddings are of relevance with respect to fuel rod integrity. The integrity of a fuel rod, in turn, is important for the fuel performance, for the safe handling of fuel rods, for the prevention of leakages and subsequent dissemination of fuel, for the avoidance of unnecessary dose rates, and for safe operation. Different factors can strongly deteriorate the mechanical fuel rod properties: irradiation damage, thermo-mechanical impact, corrosion or hydrogen uptake. To investigate the mechanical properties of fuel rod claddings which are used in Swiss nuclear power plants, PSI has initiated a program for mechanical testing. A major issue was the interaction between specific loading devices and the tested cladding tube, e.g. in the form of bending or friction. Particular for Zircaloy is the hexagonal closed packed structure of the zirconium crystallographic lattice. This structure implies plastic deformation mechanisms with specific, preferred orientations. Further, the manufacturing procedure of Zircaloy claddings induces a specific texture which plays a salient role with respect to the embrittlement by irradiation or integration of hydrogen in the form of hydrides. Both, the induced microstructure as well as the plastic deformation behaviour play a role for the mechanical properties. At PSI, in a first step inactive thin walled Zircaloy tubes and, for comparison reasons, plates were tested. The validity of the mechanical testing of the non standard tube and plate geometries had to be verified. The used Zircaloy-4 cladding tube sections and small plates of the same wall thickness have been notched, fatigue pre-cracked and tensile tested to evaluate the fracture toughness properties at room temperature, 300 {sup o}C and 350 {sup o}C. The crack propagation has been determined optically. The test results of the plates have been further used to validate FEM calculations. For each sample a complete crack resistance (J-R) curve could
International Nuclear Information System (INIS)
Zahouane, A.I.; Gauthier, J.P.; Petrequin, P.
1988-01-01
Fatigue resistance of heterogeneous welded joints between austenitic stainless steels and ferritic steels is evaluated for reactor components and more particularly effect of residual stress on fatigue crack propagation in a heterogeneous welded joint. Residual stress is measured by the hole method in which a hole is drilled through the center of a strain gage glued the surface of the materials. In the non uniform stress field a transmissibility function is used for residual stress calculation. High compression residual stress in the ferritic metal near the interface ferritic steel/weld slow down fatigue crack propagation. 5 tabs., 15 figs., 19 refs [fr
International Nuclear Information System (INIS)
Brickstad, B.
1984-01-01
Predictions of crack arrest behaviour are performed for a cracked reactor pressure vessel under both thermal and pressure loading. The object is to compare static and dynamic calculations. The dynamic calculations are made using an explicit finite element technique where crack growth is simulated by gradual nodal release. Three different load cases and the effect of different velocity dependence on the crack propagation toughness are studied. It is found that for the analysed cases the static analysis is slightly conservative, thus justifying its use for these problems. (orig.)
Topçuoğlu, Hüseyin Sinan; Düzgün, Salih; Kesim, Bertan; Tuncay, Oznur
2014-07-01
The aim of this study was to determine the incidence of crack initiation and propagation in apical root dentin after retreatment procedures performed by using 2 rotary retreatment systems and hand files with additional instrumentation. Eighty extracted mandibular premolars with single canals were selected. One millimeter from the apex of each tooth was ground perpendicular to the long axis of the tooth, and the apical surface was polished. Twenty teeth served as the control group, and no preparation was performed. The remaining 60 teeth were prepared to size 35 with rotary files and filled with gutta-percha and AH Plus sealer. Specimens were then divided into 3 groups (n = 20), and retreatment procedures were performed with the following devices and techniques: ProTaper Universal retreatment files, Mtwo retreatment files, and hand files. After retreatment, the additional instrumentation was performed by using size 40 ProTaper, Mtwo, and hand files. Digital images of the apical root surface were recorded before preparation, after instrumentation, after filling, after retreatment, and after additional instrumentation. The images were then inspected for the presence of any new apical cracks and propagation. Data were analyzed with the logistic regression and Fisher exact tests. All experimental groups caused crack initiation and propagation after use of retreatment instruments. The ProTaper and Mtwo retreatment groups caused greater crack initiation and propagation than the hand instrument group (P ProTaper and Mtwo instruments after the use of retreatment instruments caused crack initiation and propagation, whereas hand files caused neither crack initiation nor propagation (P < .05). This study showed that retreatment procedures and additional instrumentation after the use of retreatment files may cause crack initiation and propagation in apical dentin. Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Aihara, S.; Tsuchida, Y. [Nippon Steel Corp., Tokyo (Japan); Machida, S.; Yoshinari, H. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering
1996-12-31
A proposal was made previously on a model of brittle crack propagation and arrest that considers the effect of crack opening suppression by using unbroken ligaments generated on steel plate surface and the effect that cracks precede in the central part of the plate thickness, based on a local limit stress theory for brittleness fracture. This paper discusses applicability of this model to a mixed type test, and elucidates causes for difference in the arrest tenacity of both types in a double tensile test of the standard size. The brittle crack propagation and arrest model based on the local limit stress theory was found applicable to a simulation of the mixed type test. Experimental crack propagation speed history and behavior of the arrest were reproduced nearly completely by using this model. When load stress is increased, the arrests in the mixed type test may be classified into arrests of both inside the steel plate and near the surface, cracks in the former position or arrest in the latter position, and rush of cracks into both positions. Furthermore, at higher stresses, the propagation speed drops once after cracks rushed into the test plate, but turns to a rise, leading to propagation and piercing. 8 refs., 15 figs., 3 tabs.
Energy Technology Data Exchange (ETDEWEB)
Aihara, S; Tsuchida, Y [Nippon Steel Corp., Tokyo (Japan); Machida, S; Yoshinari, H [The University of Tokyo, Tokyo (Japan). Faculty of Engineering
1997-12-31
A proposal was made previously on a model of brittle crack propagation and arrest that considers the effect of crack opening suppression by using unbroken ligaments generated on steel plate surface and the effect that cracks precede in the central part of the plate thickness, based on a local limit stress theory for brittleness fracture. This paper discusses applicability of this model to a mixed type test, and elucidates causes for difference in the arrest tenacity of both types in a double tensile test of the standard size. The brittle crack propagation and arrest model based on the local limit stress theory was found applicable to a simulation of the mixed type test. Experimental crack propagation speed history and behavior of the arrest were reproduced nearly completely by using this model. When load stress is increased, the arrests in the mixed type test may be classified into arrests of both inside the steel plate and near the surface, cracks in the former position or arrest in the latter position, and rush of cracks into both positions. Furthermore, at higher stresses, the propagation speed drops once after cracks rushed into the test plate, but turns to a rise, leading to propagation and piercing. 8 refs., 15 figs., 3 tabs.
AE analysis of delamination crack propagation in carbon fiber-reinforced polymer materials
Energy Technology Data Exchange (ETDEWEB)
Yoon, Sang Jae; Arakawa, Kazuo [Kyushu University, kasuga (Japan); Chen, Dingding [National University of Defense Technology, Changsha (China); Han, Seung Wook; Choi, Nak Sam [Hanyang University, Seoul (Korea, Republic of)
2015-01-15
Delamination fracture behavior was investigated using acoustic emission (AE) analysis on carbon fiber-reinforced polymer (CFRP) samples manufactured using vacuum-assisted resin transfer molding (VARTM). CFRP plate was fabricated using unidirectional carbon fiber fabric with a lay-up of six plies [+30/-30]6 , and a Teflon film was inserted as a starter crack. Test pieces were sectioned from the inlet and vent of the mold, and packed between two rectangular epoxy plates to load using a universal testing machine. The AE signals were monitored during tensile loading using two sensors. The average tensile load of the inlet specimens was slightly larger than that of the vent specimens; however, the data exhibited significant scattering due to non-uniform resin distribution, and there was no statistically significant different between the strength of the samples sectioned from the inlet or outlet of the mold. Each of the specimens exhibited similar AE characteristics, regardless of whether they were from the inlet or vent of the mold. Four kinds of damage mechanism were observed: micro-cracking, fiber-resin matrix debonding, fiber pull-out, and fiber failure; and three stages of the crack propagation process were identified.
Reformed austenite transformation during fatigue crack propagation of 13%Cr-4%Ni stainless steel
Energy Technology Data Exchange (ETDEWEB)
Thibault, Denis, E-mail: thibault.denis@ireq.ca [Institut de recherche d' Hydro-Quebec (IREQ), 1800, boul. Lionel-Boulet, Varennes, Quebec, J3X 1S1 (Canada); Bocher, Philippe, E-mail: philippe.bocher@etsmtl.ca [Ecole de technologie superieure, 1100, rue Notre-Dame Ouest, Montreal, Quebec, H3C 1K3 (Canada); Thomas, Marc, E-mail: marc.thomas@etsmtl.ca [Ecole de technologie superieure, 1100, rue Notre-Dame Ouest, Montreal, Quebec, H3C 1K3 (Canada); Lanteigne, Jacques, E-mail: lanteigne.jacques@ireq.ca [Institut de recherche d' Hydro-Quebec (IREQ), 1800, boul. Lionel-Boulet, Varennes, Quebec, J3X 1S1 (Canada); Hovington, Pierre, E-mail: hovington.pierre@ireq.ca [Institut de recherche d' Hydro-Quebec (IREQ), 1800, boul. Lionel-Boulet, Varennes, Quebec, J3X 1S1 (Canada); Robichaud, Patrice, E-mail: patrice.robichaud@riotinto.com [Centre de recherche et de developpement Arvida (CRDA), 1955, boul. Mellon, Jonquiere, Quebec, G7S 4K8 (Canada)
2011-08-15
Highlights: {yields} Reformed austenite in 13%Cr-4%Ni stainless steel transforms during fatigue crack growth. {yields} Low cycle fatigue tests showed that this transformation to martensite is gradual. {yields} XRD spectrums obtained on the fracture surface and have been correlated to LCF results. - Abstract: In the as-quenched state, 13%Cr-4%Ni martensitic stainless steels are essentially 100% martensitic. However, a certain amount of austenite is formed during the tempering of this alloy. This reformed austenite is thermally stable at room temperature but can transform to martensite under stress. This transformation is known to happen during impact testing but it has never been established if it occurs during fatigue crack propagation. This study presents the results of X-ray diffraction measurements of reformed austenite before and after crack growth testing. It has been found that reformed austenite does transform to martensite at the crack tip and that this transformation occurs even at a low stress intensity factor. Low-cycle fatigue tests were conducted to verify austenite transformation under cyclic straining. It was found that reformed austenite transforms only partially during the first strain reversal but that essentially all austenite has disappeared after 100 cycles. The relation between austenite transformation under low-cycle fatigue and its transformation during crack growth is also discussed.
Reformed austenite transformation during fatigue crack propagation of 13%Cr-4%Ni stainless steel
International Nuclear Information System (INIS)
Thibault, Denis; Bocher, Philippe; Thomas, Marc; Lanteigne, Jacques; Hovington, Pierre; Robichaud, Patrice
2011-01-01
Highlights: → Reformed austenite in 13%Cr-4%Ni stainless steel transforms during fatigue crack growth. → Low cycle fatigue tests showed that this transformation to martensite is gradual. → XRD spectrums obtained on the fracture surface and have been correlated to LCF results. - Abstract: In the as-quenched state, 13%Cr-4%Ni martensitic stainless steels are essentially 100% martensitic. However, a certain amount of austenite is formed during the tempering of this alloy. This reformed austenite is thermally stable at room temperature but can transform to martensite under stress. This transformation is known to happen during impact testing but it has never been established if it occurs during fatigue crack propagation. This study presents the results of X-ray diffraction measurements of reformed austenite before and after crack growth testing. It has been found that reformed austenite does transform to martensite at the crack tip and that this transformation occurs even at a low stress intensity factor. Low-cycle fatigue tests were conducted to verify austenite transformation under cyclic straining. It was found that reformed austenite transforms only partially during the first strain reversal but that essentially all austenite has disappeared after 100 cycles. The relation between austenite transformation under low-cycle fatigue and its transformation during crack growth is also discussed.
Gauge-invariant approach and infrared behaviour of the spinor propagator
International Nuclear Information System (INIS)
Sisakyan, A.N.; Skachkov, N.B.; Solovtsov, I.L.; Shevchenko, O.Yu.
1989-01-01
Infrared behaviour of the gauge-invariant spinor propagator is studied. It is proved that infrared peculiarities of such a propagator can be factorized in a form of the Wilson loop that includes only the slowly varying component of electromagnetic field and accumulates all the dependence of the initial Green function of the form of the path
An analysis for crack layer stability
Sehanobish, K.; Botsis, J.; Moet, A.; Chudnovsky, A.
1986-01-01
The problem of uncontrolled crack propagation and crack arrest is considered with respect to crack layer (CL) translational stability. CL propagation is determined by the difference between the energy release rate and the amount of energy required for material transformation, and necessary and sufficient conditions for CL instability are derived. CL propagation in polystyrene is studied for two cases. For the case of remotely applied fixed load fatigue, the sufficient condition of instability is shown to be met before the necessary condition, and the necessary condition controls the stability. For the fixed displacement case, neither of the instability conditions are met, and CL propagation remains stable, resulting in crack arrest.
Energy Technology Data Exchange (ETDEWEB)
Curtit, F
2000-07-01
This study realised in LISN Laboratory of CEA Saclay, deals with the creep fatigue propagation of semi elliptical crack at the temperature of 650 deg C in 316L(N) stainless steel plates with or without welded joints. A vast majority of the studies on creep fatigue propagation models are based on specimen (CT) especially designed for crack propagation study. The PLAQFLU program performed in LISN laboratory deals with the application and adaptation of these models to complex crack shape, which are more representative of the cracks observed in industrial components. In this scope, we use propagation tests realised at the temperature of 650 deg C with wide plates containing semi elliptical defects. For some of them, the initial defect is machined in the middle of a welded joint, which constitute a privileged site for the crack initiation. The approach used in this study is based on global parameters of fracture mechanics. At first, tests on CT specimen are used in order to determine the propagation laws correlating the crack growth rate to the global parameters K or C{sup *}. These laws are then supposed to be intrinsic to our materials and are used to analysed the semi elliptical crack propagation. The analysis of the comportment of the crack during the hold time demonstrates the possibility to establish a correlation between the crack propagation both in the deepest and the surface point and the local value of C{sup *}. These correlations are coherent in the different points of the crack front for the different applied hold times, and they present a reasonably good agreement with the creep propagation law identified on CT specimen. The simulation of test performed on based metal specimen with a model of summation of both creep and pure fatigue crack growth gives acceptable results when the calculus of the simplified expression of C{sup *}{sub s} considers a continuous evolution of creep deformations rate during the all test. (author)
International Nuclear Information System (INIS)
Do, Jae Yoon; Kim, Jin Hwan; Ahn, Seok Hwan; Park, In Duck; Kang, Chang Yong; Nam, Ki Woo
2002-01-01
Because duplex stainless steel shows the good strength and corrosion resistance properties, the necessity of duplex stainless steel, which has long life in severe environments, has been increased with industrial development. The fatigue crack propagation behavior of Heat Affected Zone(HAZ) has been investigated in super duplex stainless steel. The fatigue crack propagation rate of HAZ of super duplex stainless steel was faster than that of base metal of super duplex stainless steel. We also analysed acoustic emission signals during the fatigue test with time-frequency analysis method. According to the results of time-frequency analysis, the frequency ranges of 200-400 kHz were obtained by striation and the frequency range of 500 kHz was obtained due to dimple and separate of inclusion
Investigation of Helicopter Longeron Cracks
Newman, John A.; Baughman, James; Wallace, Terryl A.
2009-01-01
Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurgical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.
Energy Technology Data Exchange (ETDEWEB)
Lee, Kwang Ho [Kyungpook National University, Daegu (Korea, Republic of); Cho, Sang Bong [Kyungnam University, Changwon (Korea, Republic of); Hawong, Jai Sug [Yeungnam University, Gyungsan (Korea, Republic of)
2015-02-15
The stress and displacement fields at the crack tip were studied during the unsteady propagation of a mode Ⅲ crack in a direction that was different from the property graduation direction in functionally graded materials (FGMs). The property graduation in FGMs was assumed based on the linearly varying shear modulus under a constant density and the exponentially varying shear modulus and density. To obtain the solution of the harmonic function, the general partial differential equation of the dynamic equilibrium equation was transformed into a Laplace equation. Based on the Laplace equation, the stress and displacement fields, which depended on the time rates of change in the crack tip speed and stress intensity factor, were obtained through an asymptotic analysis. Using the stress and displacement fields, the effects of the angled property variation on the stresses, displacements, and stress intensity factors are discussed.
The fatigue life and fatigue-crack-through-thickness behavior of a surface-cracked plate, 3
International Nuclear Information System (INIS)
Nam, Ki-Woo; Matsui, Kentaro; Ando, Kotoji; Ogura, Nobukazu
1989-01-01
The LBB (leak-before-break) design is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LNG carriers and various other structures. In the LBB design, it is necessary to evaluate precisely the lifetime of steel plate. Furthermore, the change in crack shape that occurs during the propagation after through thickness is of paramount importance. For this reason, in a previous report, the authors proposed a simplified evaluation model for the stress intensity factor after cracking through thickness. Using this model, the crack propagation behavior, crack-opening displacement and crack shape change of surface-cracked smooth specimens and surface-cracked specimens with a stress concentration were evaluated quantitatively. The present study was also done to investigate the fatigue crack propagation behavior of surface cracks subjected to combined tensile and bending stress. Estimation of fatigue crack growth was done using the Newman-Raju formula before through thickness, and using formula (7) and (8) after through thickness. Crack length a r at just through thickness increases with increasing a bending stress. Calculated fatigue crack shape showed very good agreement with experimental one. It was also found that particular crack growth behavior and change in crack shape after cracking through thickness can be explained quantitatively using the K value based on Eqs. (7) and (8). (author)
Mechanisms of stress relief cracking in titanium stabilised austenitic stainless steel
International Nuclear Information System (INIS)
Chabaud-Reytier, M.; Allais, L.; Caes, C.; Dubuisson, P.; Pineau, A.
2003-01-01
The heat affected zone (HAZ) of AISI 321 welds may exhibit a serious form of cracking during service at high temperature. This form of damage, called 'stress relief cracking', is known to be due to work hardening but also to aging due to Ti(C,N) precipitation on dislocations which modifies the mechanical behaviour of the HAZ. The present study aims to analyse the latter embrittlement mechanism in one specific heat of 321 stainless steel. To this end, different HAZs are simulated using an annealing heat-treatment, followed by various cold rolling and aging conditions. Then, we study the effects of work hardening and aging on Ti(C,N) precipitation, on the mechanical (hardness, tensile and creep) behaviour of the simulated HAZs and on their sensitivity to intergranular crack propagation through stress relaxation tests performed on pre-cracked CT type specimens tested at 600 deg. C. It is shown that work hardening is the main parameter of the involved mechanism but that aging does not promote crack initiation although it leads to titanium carbide precipitation. Therefore, the role of Ti(C,N) precipitation on stress relief cracking mechanisms is discussed. An attempt is made to show that solute drag effects are mainly responsible for this form of intergranular damage, rather than Ti(C,N) precipitation
The creep-fatigue crack growth behaviour of a 1CrMoV rotor steel
International Nuclear Information System (INIS)
Priest, R.H.; Miller, D.A.; Gladwin, D.N.; Maguire, J.
1989-01-01
Crack growth rates under simultaneous creep-fatigue conditions have been quantified for a 1CrMoV rotor steel. Measured growth rates were partitioned into cyclic and hold period contributions and these characterized by the relevant fracture mechanics parameters K and C. Cyclic growth rates measured in the creep-fatigue tests were enhanced compared with pure fatigue rates. This observation is compared with the behaviour of other steels and explained by quantitative metallography. The resulting crack growth equation can be used during integrity assessments for plant components containing cracks which are subject to thermal fatigue
Zirconium alloy fuel cladding resistant to PCI crack propagation
International Nuclear Information System (INIS)
Boyle, R.F.; Foster, J.P.
1987-01-01
A nuclear fuel element is described cladding tube comprising: concentric tubular layers of zirconium base alloys; the concentric tubular layers including an inner layer and outer layer; the outer layer metallurgically bonded to the inner layer; the outer layer composed of a first zirconium base alloy characterized by excellent resistance to corrosion caused by exposure to high temperature and pressure aqueous environments; the inner layer composed of a second zirconium base alloy consisting of: about 0.2 to 0.6 wt.% tin, about 0.03 to 0.11 wt.% iron, less than about 0.02 wt.% chromium, up to about 350 ppm oxygen and the remainder being zirconium and incidental impurities, and the inner layer characterized by improved resistance to crack propagation under reactor operating conditions compared to the first zirconium alloy
Dynamic behaviour of the icosahedral Al–Pd–Mn quasicrystal with a Griffith crack
International Nuclear Information System (INIS)
Xiao-Fang, Wang; Ai-Yu, Zhu; Tian-You, Fan
2009-01-01
The dynamic response of an icosahedral Al–Pd–Mn quasicrystal with a Griffith crack to impact loading is investigated in this paper. The elastohydrodynamic model for the wave propagation and diffusion together with their interaction is adopted. Numerical results of stress, displacement and dynamic stress intensity factors are obtained by using the finite difference method. The effects of wave propagation, diffusion and phonon–phason coupling on the quasicrystal in the dynamic process are discussed in detail, where the phason dynamics is explored particularly. (condensed matter: structure, thermal and mechanical properties)
International Nuclear Information System (INIS)
Ritter, S.; Seifert, H.P.
2008-01-01
The low-frequency corrosion fatigue (CF) crack growth behaviour of different low-alloy reactor pressure vessel steels was characterized under simulated boiling water reactor conditions by cyclic fatigue tests with pre-cracked fracture mechanics specimens. The experiments were performed in the temperature range of 240-288 deg. C with different loading parameters at different electrochemical corrosion potentials (ECPs). Modern high-temperature water loops, on-line crack growth monitoring (DCPD) and fractographical analysis by SEM were used to quantify the cracking response. In this paper the effect of ECP on the CF crack growth behaviour is discussed and compared with the crack growth model of General Electric (GE). The ECP mainly affected the transition from fast ('high-sulphur') to slow ('low-sulphur') CF crack growth, which appeared as critical frequencies ν crit = f(ΔK, R, ECP) and ΔK-thresholds ΔK EAC f(ν, R, ECP) in the cycle-based form and as a critical air fatigue crack growth rate da/dt Air,crit in the time-domain form. The critical crack growth rates, frequencies, and ΔK EAC -thresholds were shifted to lower values with increasing ECP. The CF crack growth rates of all materials were conservatively covered by the 'high-sulphur' CF line of the GE-model for all investigated temperatures and frequencies. Under most system conditions, the model seems to reasonably well predict the experimentally observed parameter trends. Only under highly oxidizing conditions (ECP ≥ 0 mV SHE ) and slow strain rates/low loading frequencies the GE-model does not conservatively cover the experimentally gathered crack growth rate data. Based on the GE-model and the observed cracking behaviour a simple time-domain superposition-model could be used to develop improved reference CF crack growth curves for codes
Directory of Open Access Journals (Sweden)
Ahmad S.R.
2017-01-01
Full Text Available The objective of this study is to evaluate the application of the metal magnetic memory (MMM technique for investigations on fatigue crack propagation in a ferromagnetic material. Fatigue failure caused by stress concentration is serious in practical engineering. However, early fatigue damages cannot be detected by using traditional nondestructive testing (NDT methods. Therefore this paper study about NDT method called metal magnetic memory (MMM that has potentials for evaluating the fatigue damage at the early damage and critical fracture stages. While its capacity to evaluate the distribution of self-magnetic leakage field signals on the component’s surface is well-established, there remains a need to scrutinize the physical mechanism and quantitative analysis aspects of this method. To begin with, a fatigue test involving a loading of 7kN was conducted on a SAE 1045 carbon steel specimen. This material is frequently used in the manufacturing of automotive transmission components that include the axle and spline shaft. MMM signals were measured along a scanning distance of 100 mm and analysed during the propagation stage. Other than revealing that the value of the magnetic flux gradient signals dH(y/dx increased in tandem with the crack length, the results also led to the detection of the crack growth location. It was anticipated that the dH(y/dx value will also exhibit an upward trend with a rise in the fatigue growth rate of da/dN. A modified Paris equation was utilized to correlate dH(y/dx with da/dn through the replacement of the stress intensity factor range ΔK. This resulted in the log-log plot of da/dN versus dH(y/dx portraying an inclination similar to the log-log plot of da/dN versus ΔK. A linear relationship was established between dH(y/dx and ΔK with the R2 value as 0.96. Players in the automotive industry can benefit from the disclosure that dH(y/dx can effectively replace ΔK for the monitoring of fatigue crack growth
International Nuclear Information System (INIS)
Stoeckl, H.
1991-06-01
Numerical simulations of fracture-mechanical experiments with the aim of determining the stress intensity factor and its relation to the fracture velocity from the measured data of the crack length are problematic with the conventional DCB specimen loaded through wedge and bolt namely because of the not clearly definable limiting conditions. Experiments were therefore carried out with modified DCB specimens made of ARALDIT B, with the loading wedge pressed directly into the crack mouth. In the case of suitable specimen dimensions, K I already in the initial phase of crack propagation before arrival of the first reflected waves covers a great part of the relevant range. Numerical simulations agree well with the shadow-optical measurements in this phase. A specimen variant with T-shaped extension at the counterbearing is suitable especially for crack arrest investigations, since high fracture velocities and brief crack jump lengths can be combined in tests with this specimen. The constant member in the series development of the stress distribution at the crack tip according to Williams determines the directional stability of the crack. The theories established by Cotterell, Schindler, Streit and Finnie are discussed by means of the kinking cracks observed during some experiments. (orig.) [de
3-D analysis of fatigue crack behaviour in a shot peened steam turbine blade material
Energy Technology Data Exchange (ETDEWEB)
He, B.Y., E-mail: Binyan.he@soton.ac.uk [Engineering Materials, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Katsamenis, O.L. [muVIS X-ray Imaging Centre, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Mellor, B.G.; Reed, P.A.S. [Engineering Materials, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom)
2015-08-26
Serial mechanical sectioning and high resolution X-ray tomography have been used to study the three-dimensional morphology of small fatigue cracks growing in a 12 Cr tempered martensitic steam turbine blade material. A range of surface conditions has been studied, namely polished and shot peened (with varying levels of intensity). In the polished (unpeened) condition, inclusions (alumina and manganese sulphide) played an important role in initiating and controlling early fatigue crack behaviour. When fatigue cracks initiated from an alumina stringer, the crack morphology was normally dominated by single stringers, which were always in the centre of the fatigue crack, indicating its primary role in initiation. Manganese sulphide inclusion groups however seemed to dominate and affect the crack path along both the surface and depth crack growth directions. The more intensely shot peened condition did not however evidence inclusion or stringer affected fatigue crack initiation or growth behaviour; sub-surface crack coalescence being clearly observed by both serial sectioning and computed tomography (CT) imaging techniques at a depth of about 150–180 μm. These sub-surface crack coalescences can be linked to both the extent of the compressive residual stress as well as the depth of the plastic deformation arising from the intense shot peening process. Shot peening appears to provide a different defect population that initiates fatigue cracks and competes with the underlying metallurgical defect populations. The most beneficial shot peening process would in this case appear to “deactivate” the original metallurgical defect population and substitute a known defect distribution from the shot peening process from which fatigue cracks grow rather slowly in the strain hardened surface layer which also contains compressive residual stresses. A benefit to fatigue life in bending, even under Low Cycle Fatigue (LCF) conditions, has been observed in these tests if a
Beyea, S D; Balcom, B J; Bremner, T W; Prado, P J; Cross, A R; Armstrong, R L; Grattan-Bellew, P E
1998-11-01
The removal of water from pores in hardened cement paste smaller than 50 nm results in cracking of the cement matrix due to the tensile stresses induced by drying shrinkage. Cracks in the matrix fundamentally alter the permeability of the material, and therefore directly affect the drying behaviour. Using Single-Point Imaging (SPI), we obtain one-dimensional moisture profiles of hydrated White Portland cement cylinders as a function of drying time. The drying behaviour of White Portland cement, is distinctly different from the drying behaviour of related concrete materials containing aggregates.
International Nuclear Information System (INIS)
Goel, V.S.
1985-01-01
This book presents the papers given at a conference on alloy corrosion cracking. Topics considered at the conference included the effect of niobium addition on intergranular stress corrosion cracking, corrosion-fatigue cracking in fossil-fueled-boilers, fracture toughness, fracture modes, hydrogen-induced thresholds, electrochemical and hydrogen permeation studies, the effect of seawater on fatigue crack propagation of wells for offshore structures, the corrosion fatigue of carbon steels in seawater, and stress corrosion cracking and the mechanical strength of alloy 600
Energy Technology Data Exchange (ETDEWEB)
Youseffi, K.; Finnie, I.
1978-02-01
The fatigue crack initiation life of AISI 1018 steel was investigated using compact tension specimens having sharp notch root radii. The data were analyzed using two methods for predicting initiation in strain cycling experiments. Also, another approach in which initiation is related to the stress intensity factor was developed. The next phase, that of propagation, was studied using AISI 1018 steel and a new high strength steel HY-180. The crack propagation data obtained for both steels tested in air can be described accurately by the power law first suggested by Paris, da/dN = C(..delta..K)/sup n/, where a is the crack length, N the number of cycles, and C and n are material constants. However, the exponent n was found to be two times larger for AISI 1018 steel than HY-180 steel.
International Nuclear Information System (INIS)
Youseffi, K.; Finnie, I.
1978-02-01
The fatigue crack initiation life of AISI 1018 steel was investigated using compact tension specimens having sharp notch root radii. The data were analyzed using two methods for predicting initiation in strain cycling experiments. Also, another approach in which initiation is related to the stress intensity factor was developed. The next phase, that of propagation, was studied using AISI 1018 steel and a new high strength steel HY-180. The crack propagation data obtained for both steels tested in air can be described accurately by the power law first suggested by Paris, da/dN = C(ΔK)/sup n/, where a is the crack length, N the number of cycles, and C and n are material constants. However, the exponent n was found to be two times larger for AISI 1018 steel than HY-180 steel
Molecular dynamics simulations of quasi-brittle crack development in iron
Energy Technology Data Exchange (ETDEWEB)
Borodin, V.A., E-mail: borodin@dni.polin.kiae.su [Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany); NRC Kurchatov Institute, Kurchatov Sq. 1, 123182 Moscow (Russian Federation); Vladimirov, P.V., E-mail: Pavel.Vladimirov@kit.edu [Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany)
2011-08-31
The paper presents the results of molecular dynamics (MD) simulations of three-dimensional kinetics of micro-crack propagation in alpha-iron and the accompanying lattice transformations at the crack tips. We show that crack initiation on {l_brace}0 0 1{r_brace} planes in iron is preceded with the emission of compact slip bands from the pre-crack tips, in agreement with the predictions of the earlier quasi-two-dimensional simulations. The application of Voronoi decomposition technique for atomic short-range order processing has allowed us to clarify the kinetics of structural transformations at the tips of nucleating and propagating cracks for three most common systems of crack propagation in iron. It is demonstrated that the compact slip bands emanating from the crack tips not only accompany crack nucleation, but remain an essential feature of the crack propagation on {l_brace}0 0 1{r_brace} planes. Due to the strong coupling between the crack tip and slip band propagation, the crack propagation can be limited by slip band interaction with microstructural obstacles, abundantly created in ferritic-martensitic steels in radiation environment of nuclear facilities.
Energy Technology Data Exchange (ETDEWEB)
Pedron, J P; Pineau, A
1982-11-01
The crack growth properties of various microstructures developed in one heat of Inconel 718 alloy were investigated at 650/sup 0/C under air and vacuum environments. The microstructures included fine-grained material (ASTM grain sizes 6-8), coarse-grained material (ASTM grain sizes 3-4) and material of a necklace structure (ASTM grain sizes 3-4 and 8-10). The effect of grain boundary ..beta.. (Ni/sub 3/Nb) phase precipitation was also studied. Continuous fatigue, creep and creep-fatigue conditions were examined. For continuous fatigue the influence of frequency was investigated over the range between 5x10/sup -2/ and 20 Hz. For creep-fatigue conditions, hold times of 10 and 300 s were superimposed on a 5x10/sup -2/ Hz triangular wave shape signal. It was shown that the grain boundary microstructure had a very strong effect when the fatigue crack propagation behaviour was essentially time dependent. This effect is associated with the occurrence of brittle intergranular fracture and dramatic increases in crack growth rate. The microstructure had no effect under vacuum testing.
On governing equations for crack layer propagation
Chudnovsky, A.; Botsis, J.
1988-01-01
Results of analysis on damage distribution of a crack layer, in a model material, supported the self-similarity hypothesis of damage evolution which has been adopted by the crack layer theory. On the basis of measurements of discontinuity density and the double layer potential technique, a solution to the crack damage interaction problem has been developed. Evaluation of the stress intensity factor illustrated the methodology. Analysis of experimental results showed that Arrhenius type constitutive relationship described very well the expansion of the active zone of a crack layer.
Energy Technology Data Exchange (ETDEWEB)
Assire, A
2000-10-13
. Concerning local approach, intergranular creep damage model of the Ecole des Mines de Paris is used for crack initiation and growth under creep and creep fatigue loading. Crack propagations are simulated with an adaptive re-meshing technique and are compared with experimental results for crack located in weld and base metal. A sensibility analysis shows that crack propagation strongly depend on the characteristic distance, which is needed to simulate crack growth with local approach, for the weld metal parameters. (author)
Probabilistic modeling of crack networks in thermal fatigue
International Nuclear Information System (INIS)
Malesys, N.
2007-11-01
Thermal superficial crack networks have been detected in mixing zone of cooling system in nuclear power plants. Numerous experimental works have already been led to characterize initiation and propagation of these cracks. The random aspect of initiation led to propose a probabilistic model for the formation and propagation of crack networks in thermal fatigue. In a first part, uniaxial mechanical test were performed on smooth and slightly notched specimens in order to characterize the initiation of multiple cracks, their arrest due to obscuration and the coalescence phenomenon by recovery of amplification stress zones. In a second time, the probabilistic model was established under two assumptions: the continuous cracks initiation on surface, described by a Poisson point process law with threshold, and the shielding phenomenon which prohibits the initiation or the propagation of a crack if this one is in the relaxation stress zone of another existing crack. The crack propagation is assumed to follow a Paris' law based on the computation of stress intensity factors at the top and the bottom of crack. The evolution of multiaxial cracks on the surface can be followed thanks to three quantities: the shielding probability, comparable to a damage variable of the structure, the initiated crack density, representing the total number of cracks per unit surface which can be compared to experimental observations, and the propagating crack density, representing the number per unit surface of active cracks in the network. The crack sizes distribution is also computed by the model allowing an easier comparison with experimental results. (author)
Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads
International Nuclear Information System (INIS)
Han, Jeong Woo; Woo, Eun Taek; Han, Seung Ho
2015-01-01
To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka’s equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka’s equation, and the Paris’ equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%
Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads
Energy Technology Data Exchange (ETDEWEB)
Han, Jeong Woo [KIMM, Daejeon (Korea, Republic of); Woo, Eun Taek; Han, Seung Ho [Dong-A University, Busan (Korea, Republic of)
2015-07-15
To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka’s equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka’s equation, and the Paris’ equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%.
International Nuclear Information System (INIS)
Murakami, Ri-ichi; Akizono, Koichi; Kusukawa, Kazuhiro.
1988-01-01
The fatigue crack propagation behavior in fatigue impact at room temperature and 103 K was investigated by means of fracture mechanics, X-ray diffraction analysis and fractography for an austenitic stainless steel, SUS 304. The crack growth rate in fatigue impact decreased with decreasing temperature. The crack growth rate at room temperature was scarcely influenced by the microstructure, while at low temperature it was markedly influenced by the microstructure. The effects of microstructure and temperature on the crack growth rate were closely related to the strain-induced martensitic transformation. The martensitic transformation was influenced by the microstructure, the temperature, the fracture morphology and the stress intensity level and resulted in a decrease in crack growth rate with increasing crack opening level. (author)
International Nuclear Information System (INIS)
Seifert, H.P.; Ritter, S.; Leber, H.J.
2012-01-01
Highlights: ► Corrosion fatigue in austenitic stainless steels under light water reactor conditions. ► Identification of major parameters of influence on initiation and short crack growth. ► Critical system conditions for environmental reduction of fatigue initiation life. ► Comparison with the environmental factor (F env ) approach. - Abstract: The corrosion fatigue initiation and short crack growth behaviour of different wrought low-carbon and stabilised austenitic stainless steels was characterised under simulated boiling water reactor and pressurised water reactor primary water conditions by cyclic fatigue tests with sharply notched fracture mechanics specimens. The special emphasis was placed to the behaviour at low corrosion potentials and, in particular, to hydrogen water chemistry conditions. The major parameter effects and critical conjoint threshold conditions, which result in relevant environmental reduction and acceleration of fatigue initiation life and subsequent short crack growth, respectively, are discussed and summarised. The observed corrosion fatigue behaviour is compared with the fatigue evaluation procedures in codes and regulatory guidelines.
Role of hydrogen in stress corrosion cracking
International Nuclear Information System (INIS)
Mehta, M.L.
1981-01-01
Electrochemical basis for differentiation between hydrogen embrittlement and active path corrosion or anodic dissolution crack growth mechanisms is examined. The consequences of recently demonstrated acidification in crack tip region irrespective of electrochemical conditions at the bulk surface of the sample are that the hydrogen can evolve within the crack and may be involved in the cracking process. There are basically three aspects of hydrogen involvement in stress corrosion cracking. In dissolution models crack propagation is assumed to be caused by anodic dissolution on the crack tip sustained by cathodic reduction of hydrogen from electrolyte within the crack. In hydrogen induced structural transformation models it is postulated that hydrogen is absorbed locally at the crack tip producing structural changes which facilitate crack propagation. In hydrogen embrittlement models hydrogen is absorbed by stressed metal from proton reduction from the electrolyte within the crack and there is interaction between lattice and hydrogen resulting in embrittlement of material at crack tip facilitating crack propagation. In the present paper, the role of hydrogen in stress corrosion crack growth in high strength steels, austenitic stainless steels, titanium alloys and high strength aluminium alloys is discussed. (author)
Fatigue-crack propagation response of two nickel-base alloys in a liquid sodium environment
International Nuclear Information System (INIS)
Mills, W.J.; James, L.A.
1979-01-01
The elevated temperature fatigue-crack propagation response of Inconel 600 and Inconel 718 was characterized within a linear-elastic fracture mechanics framework in air and low-oxygen liquid sodium environments. The crack growth rates of both nickel-base alloys tested in liquid sodium were found to be considerably lower than those obtained in air. This enhanced fatigue resistance in sodium was attributed to the very low oxygen content in the inert sodium environment. Electron fractographic examination of the Inconel 600 and Inconel 718 fatigue fracture surfaces revealed that operative crack growth mechanisms were dependent on the prevailing stress intensity level. Under low growth rate conditions, Inconel 600 and Inconel 718 fracture surfaces exhibited a faceted, crystallographic morphology in both air and sodium environments. In the higher growth rate regime, fatigue striations were observed; however, striations formed in sodium were rather ill-defined. These indistinct striations were attributed to the absence of oxygen in the liquid sodium environment. Striation spacing measurements were found to be in excellent agreement with macroscopic growth rates in both environments
On the influence of microscale inertia on dynamic ductile crack extension
Jacques, N.; Mercier, S.; Molinari, A.
2012-08-01
The present paper is devoted to the modelling of damage by micro-voiding in ductile solids under dynamic loading conditions. Using a dynamic homogenization procedure, a constitutive damage model accounting for inertial effects due to void growth (microscale inertia or micro-inertia) has been developed. The role played by microscale inertia in dynamic ductile crack growth is investigated with the use of the proposed micromechanical modelling. It is found that micro-inertia has a significant influence on the fracture behaviour. Micro-inertia limits the velocity at which cracks propagate. It also contributes to increase the apparent dynamic toughness of the material.
International Nuclear Information System (INIS)
Tao, Junhui; Hu, Shubing; Ji, Longbo
2016-01-01
In this paper, we describe experiments on welded joints of Ti-6Al-4V alloy specimens exhibiting fatigue characteristics in the base metal (BM), hot affected zone (HAZ) and fuse zone (FZ). The effect of micromorphology on crack propagation at the tip of the fatigue crack in joints formed by electron beam welding was investigated using an optical microscope, transmission electron microscope and other methodologies. The results demonstrated that the fatigue crack originated in and propagated along α/β boundaries in the BM. In the HAZ, the fatigue crack occurred at the boundary between martensite laths, and propagated through most irregular-equiaxed α phases and a few martensite laths. In the FZ, the fatigue crack originated at the boundaries between the fine crushing phases among martensite laths, and propagated along a majority of α/β boundaries and several narrow martensite laths. The electron beam welded joint of Ti-6Al-4V alloy showed instances of zigzag fatigue cracks that increased in degree from lowest in the HAZ, moderate in the FZ to greatest in the BM. Conversely, fatigue crack growth rate (FCGR) was greatest in the HAZ, less in the FZ and slowest in the BM. - Highlights: •Ti-6Al-4V welded joint exhibits different fatigue characteristics. •The fatigue crack propagates along α/β boundaries in the BM. •The fatigue crack propagates through α phases and martensite laths in the HAZ. •The fatigue crack propagates along α/β boundaries and martensite laths in the FZ. •Fatigue crack growth rate is fastest in the HAZ, less in the FZ, slowest in the BM.
International Nuclear Information System (INIS)
Haddar, N.
2003-04-01
The elbow pipes of thermal plants cooling systems are submitted to thermal variations of short range and of variable frequency. These variations bound to temperature changes of the fluids present a risk of cracks and leakages. In order to solve this problem, EDF has started the 'CRECO RNE 808' plan: 'thermal fatigue of 304L austenitic stainless steels' to study experimentally on a volume part, the initiation and the beginning of the propagation of cracks in thermal fatigue on austenitic stainless steels. The aim of this study is more particularly to compare the behaviour and the damage of the material in mechanic-thermal fatigue (cycling in temperature and cycling in deformation) and in isothermal fatigue (the utmost conditions have been determined by EDF for the metal: Tmax = 165 degrees C and Tmin = 90 degrees C; the frequency of the thermal variations can reach a Hertz). A lot of experimental results are given. A model of lifetime is introduced and validated. (O.M.)
International Nuclear Information System (INIS)
Zhong Yong; Xiao Furen; Zhang Jingwu; Shan Yiyin; Wang Wei; Yang Ke
2006-01-01
Microstructural refinement of structural materials generally improves their tensile properties but deteriorates their fatigue properties. However, pipeline steels with ultra-fine acicular ferrite (UFAF) possess not only high strength and toughness, but also a low fatigue-crack-growth rate (FCGR) and long fatigue-propagation life. In this paper, the micro-fracture mechanisms of an UFAF pipeline steel are investigated by in situ tensile testing in a transmission electron microscope. The results indicate that a grain-boundary-film structure composed of martensite/austenite could significantly influence the crack propagating behavior in the UFAF steel, consequently lowering the FCGR by enhancing roughness-induced crack closure during cyclic loading
Fatigue crack detection and identification by the elastic wave propagation method
Stawiarski, Adam; Barski, Marek; Pająk, Piotr
2017-05-01
In this paper the elastic wave propagation phenomenon was used to detect the initiation of the fatigue damage in isotropic plate with a circular hole. The safety and reliability of structures mostly depend on the effectiveness of the monitoring methods. The Structural Health Monitoring (SHM) system based on the active pitch-catch measurement technique was proposed. The piezoelectric (PZT) elements was used as an actuators and sensors in the multipoint measuring system. The comparison of the intact and defected structures has been used by damage detection algorithm. One part of the SHM system has been responsible for detection of the fatigue crack initiation. The second part observed the evolution of the damage growth and assess the size of the defect. The numerical results of the wave propagation phenomenon has been used to present the effectiveness and accuracy of the proposed method. The preliminary experimental analysis has been carried out during the tension test of the aluminum plate with a circular hole to determine the efficiency of the measurement technique.
Mohammadi, H; Klassen, R J; Wan, W-K
2008-10-01
Pyrolytic carbon mechanical heart valves (MHVs) are widely used to replace dysfunctional and failed heart valves. As the human heart beats around 40 million times per year, fatigue is the prime mechanism of mechanical failure. In this study, a finite element approach is implemented to develop a model for fatigue analysis of MHVs due to the impact force between the leaflet and the stent and cavitation in the aortic position. A two-step method to predict crack propagation in the leaflets of MHVs has been developed. Stress intensity factors (SIFs) are computed at a small initiated crack located on the leaflet edge (the worst case) using the boundary element method (BEM). Static analysis of the crack is performed to analyse the stress distribution around the front crack zone when the crack is opened; this is followed by a dynamic crack analysis to consider crack propagation using the finite element approach. Two factors are taken into account in the calculation of the SIFs: first, the effect of microjet formation due to cavitation in the vicinity of leaflets, resulting in water hammer pressure; second, the effect of the impact force between the leaflet and the stent of the MHVs, both in the closing phase. The critical initial crack length, the SIFs, the water hammer pressure, and the maximum jet velocity due to cavitation have been calculated. With an initial crack length of 35 microm, the fatigue life of the heart valve is greater than 60 years (i.e. about 2.2 x 10(9) cycles) and, with an initial crack length of 170 microm, the fatigue life of the heart valve would be around 2.5 years (i.e. about 9.1 x 10(7) cycles). For an initial crack length greater than 170 microm, there is catastrophic failure and fatigue cracking no longer occurs. A finite element model of fatigue analysis using Patran command language (PCL custom code) in MSC software can be used to evaluate the useful lifespan of MHVs. Similar methodologies can be extended to other medical devices under cyclic
International Nuclear Information System (INIS)
Calonne, V.
2001-07-01
Duplex stainless steels are used as cast components in nuclear power plants. At the service temperature of about 320 C, the ferrite phase is thermally aged and embrittled. This induces a significant decrease in fracture properties of these materials. The aim of this work consists in studying Fatigue Crack Growth Rates (FCGR) and Fatigue Crack Growth Mechanisms (FCGM) as a function of thermal ageing and test temperature (20 C/320 C). Two cast duplex stainless steels (30% ferrite) are tested. In order to better understand the influence of the crystallographic orientation of the phases on the FCGM, the solidification structure of the material is studied by Electron Back-Scatter Diffraction (EBSD) and by Unidirectional Solidification Quenching. Fatigue crack growth tests are also performed in equiaxed and basaltic structures. Microstructure, fatigue crack growth mechanical properties and mechanisms are thus studied in relation to each other. In the studied range of delta K, the crack propagates without any preferential path by successive ruptures of phase laths. The macroscopic crack propagation plane, as determined by EBSD, depends on the crystallographic orientation of the ferrite grain. So, according to the solidification structure, secondary cracks can appear, which in turn influences the FCGR. Fatigue crack closure, which has to be determined to estimate the intrinsic FCGR, decreases with increasing ageing. This can be explained by a decrease in the kinematic cyclic hardening. The Paris exponent as determined from intrinsic FCGR increases with ageing. Intrinsic FCGR can then be separated in two ranges: one with lower FCGR in aged materials than in un-aged and one with the reversed tendency. (author)
Zhang, Wei; Bao, Zhangmin; Jiang, Shan; He, Jingjing
2016-06-17
In the aerospace and aviation sectors, the damage tolerance concept has been applied widely so that the modeling analysis of fatigue crack growth has become more and more significant. Since the process of crack propagation is highly nonlinear and determined by many factors, such as applied stress, plastic zone in the crack tip, length of the crack, etc. , it is difficult to build up a general and flexible explicit function to accurately quantify this complicated relationship. Fortunately, the artificial neural network (ANN) is considered a powerful tool for establishing the nonlinear multivariate projection which shows potential in handling the fatigue crack problem. In this paper, a novel fatigue crack calculation algorithm based on a radial basis function (RBF)-ANN is proposed to study this relationship from the experimental data. In addition, a parameter called the equivalent stress intensity factor is also employed as training data to account for loading interaction effects. The testing data is then placed under constant amplitude loading with different stress ratios or overloads used for model validation. Moreover, the Forman and Wheeler equations are also adopted to compare with our proposed algorithm. The current investigation shows that the ANN-based approach can deliver a better agreement with the experimental data than the other two models, which supports that the RBF-ANN has nontrivial advantages in handling the fatigue crack growth problem. Furthermore, it implies that the proposed algorithm is possibly a sophisticated and promising method to compute fatigue crack growth in terms of loading interaction effects.
Directory of Open Access Journals (Sweden)
Y. Besel
2016-01-01
Full Text Available The influence of the joint line remnant (JLR on tensile and fatigue fracture behaviour has been investigated in a friction stir welded Al-Mg-Sc alloy. JLR is one of the microstructural features formed in friction stir welds depending on welding conditions and alloy systems. It is attributed to initial oxide layer on butting surfaces to be welded. In this study, two different tool travel speeds were used. JLR was formed in both welds but its spatial distribution was different depending on the tool travel speeds. Under the tensile test, the weld with the higher heat input fractured partially along JLR, since strong microstructural inhomogeneity existed in the vicinity of JLR in this weld and JLR had weak bonding. Resultantly, the mechanical properties of this weld were deteriorated compared with the other weld. Fatigue crack initiation was not affected by the existence of JLR in all welds. But the crack propagated preferentially along JLR in the weld of the higher heat input, when it initiated on the retreating side. Consequently, such crack propagation behaviour along JLR could bring about shorter fatigue lives in larger components in which crack growth phase is dominant.
Energy Technology Data Exchange (ETDEWEB)
James, L A
1986-01-01
Fatigue-crack propagation tests were conducted in air at 538/sup 0/C on several specimens of Alloy 718 representing several different producers, melt practices and product forms. This variety resulted in a range of grain sizes from ASTM Size 5 to 11.5. Tests at low cyclic frequency employing a tensile hold-time revealed a relationship between crack growth rates and grain size: higher growth rates were associated with fine-grain material and lower rates with larger-grain material. The lowest crack growth rates were associated with a necklace microstructure, whereby large grains are associated with necklaces of very small grains.
Çapar, İsmail Davut; Uysal, Banu; Ok, Evren; Arslan, Hakan
2015-02-01
The purpose of this study was to investigate the incidence of apical crack initiation and propagation in root dentin after several endodontic procedures. Sixty intact mandibular premolars were sectioned perpendicular to the long axis at 1 mm from the apex, and the apical surface was polished. Thirty teeth were left unprepared and served as a control, and the remaining 30 teeth were instrumented with ProTaper Universal instruments (Dentsply Maillefer, Ballaigues, Switzerland) up to size F5. The root canals were filled with the single-cone technique. Gutta-percha was removed with drills of the Rebilda post system (VOCO, Cuxhaven, Germany). Glass fiber-reinforced composite fiber posts were cemented using a dual-cure resin cement. The fiber posts were removed with a drill of the post system. Retreatment was completed after the removal of the gutta-percha. Crack initiation and propagation in the apical surfaces of the samples were examined with a stereomicroscope after each procedure. The absence/presence of cracks was recorded. Logistic regression was performed to analyze statistically the incidence of crack initiation and propagation with each procedure. The initiation of the first crack and crack propagation was associated with F2 and F4 instruments, respectively. The logistic regression analysis revealed that instrumentation and F2 instrument significantly affected apical crack initiation (P .05). Rotary nickel-titanium instrumentation had a significant effect on apical crack initiation, and post space preparation with drills had a significant impact on crack propagation. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.
High temperature cracking of steels: effect of geometry on creep crack growth laws
International Nuclear Information System (INIS)
Kabiri, M.R.
2003-12-01
This study was performed at Centre des Materiaux de l'Ecole des Mines de Paris. It deals with identification and transferability of high temperature creep cracking laws of steels. A global approach, based on C * and J non-linear fracture mechanics parameters has been used to characterize creep crack initiation and propagation. The studied materials are: the ferritic steels 1Cr-1Mo-1/4V (hot and cold parts working at 540 and 250 C) used in the thermal power stations and the austenitic stainless steel 316 L(N) used in the nuclear power stations. During this thesis a data base was setting up, it regroups several tests of fatigue, creep, creep-fatigue, and relaxation. Its particularity is to contain several creep tests (27 tests), achieved at various temperatures (550 to 650 C) and using three different geometries. The relevance of the C * parameter to describe the creep crack propagation was analysed by a means of systematic study of elasto-viscoplastic stress singularities under several conditions (different stress triaxiality). It has been shown that, besides the C * parameter, a second non singular term, denoted here as Q * , is necessary to describe the local variables in the vicinity of the crack tip. Values of this constraint parameter are always negative. Consequently, application of typical creep crack growth laws linking the creep crack growth rate to the C * parameter (da/dt - C * ), will be conservative for industrial applications. Furthermore, we showed that for ferritic steels, crack incubation period is important, therefore a correlation of Ti - C * type has been kept to predict crack initiation time Ti. For the austenitic stainless steel, the relevant stage is the one of the crack propagation, so that a master curve (da/dt - C * ), using a new data analysis method, was established. Finally, the propagation of cracks has been simulated numerically using the node release technique, allowing to validate analytical expressions utilised for the experimental
Investigation of Cracks Found in Helicopter Longerons
Newman, John A.; Baughman, James M.; Wallace, Terryl A.
2009-01-01
Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurigical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.
International Nuclear Information System (INIS)
Lloyd, G.J.; Wareing, J.
1979-01-01
The distinction between stable and unstable fatigue crack propagation during high temperature creep-fatigue in austenitic stainless steels is introduced. The transition from one class of behavior to the other is related to the precipitate distribution and to the nature of the prevailing crack path. It is shown by reference to new studies and examples drawn from the literature that this behavior is common to both high strain and predominantly elastic fatigue in austenitic stainless steels. The relevance of this distinction to a mechanistic approach to high temperature plant design is discussed
DEFF Research Database (Denmark)
Sonne, Mads Rostgaard; Carlone, P.; Citarella, R.
2015-01-01
This paper deals with a numerical and experimental investigation on the influence of residual stresses on fatigue crack growth in AA2024-T3 friction stir welded butt joints. An integrated FEM-DBEM procedure for the simulation of crack propagation is proposed and discussed. A numerical FEM model...... of the welding process of precipitation hardenable AA2024-T3 aluminum alloy is employed to infer the process induced residual stress field. The reliability of the FEM simulations with respect to the induced residual stresses is assessed comparing numerical outcomes with experimental data obtained by means...
Delayed hydrogen cracking test design for pressure tubes
International Nuclear Information System (INIS)
Haddad, Roberto; Loberse, Antonio N.; Yawny, Alejandro A.; Riquelme, Pablo
1999-01-01
CANDU nuclear power stations pressure tubes of alloy Zr-2,5 % Nb present a cracking phenomenon known as delayed hydrogen cracking (DHC). This is a brittle fracture of zirconium hydrides that are developed by hydrogen due to aqueous corrosion on the metal surface. This hydrogen diffuses to the crack tip where brittle zirconium hydrides develops and promotes the crack propagation. A direct current potential decay (DCPD) technique has been developed to measure crack propagation rates on compact test (CT) samples machined from a non irradiated pressure tube. Those test samples were hydrogen charged by cathodic polarization in an acid solution and then pre cracked in a fatigue machine. This technique proved to be useful to measure crack propagation rates with at least 1% accuracy for DHC in pressure tubes. (author)
Energy Technology Data Exchange (ETDEWEB)
Assire, A
2000-10-13
results. Concerning local approach, intergranular creep damage model of the Ecole des Mines de Paris is used for crack initiation and growth under creep and creep fatigue loading. Crack propagations are simulated with an adaptive re-meshing technique and are compared with experimental results for crack located in weld and base metal. A sensibility analysis shows that crack propagation strongly depend on the characteristic distance, which is needed to simulate crack growth with local approach, for the weld metal parameters. (author)
Das, A.; Viehrig, H. W.; Bergner, F.; Heintze, C.; Altstadt, E.; Hoffmann, J.
2017-08-01
ODS steels have been known to exhibit anisotropic fracture behaviour and form secondary cracks. In this work, the factors responsible for the anisotropic fracture behaviour have been investigated using scanning electron microscopy and electron backscatter microscopy. Fracture toughness of hot rolled 13Cr ODS steel was determined using unloading compliance method for L-T and T-L orientations at various temperatures. L-T orientation had higher fracture toughness than T-L orientation and also contained more pronounced secondary cracking. Secondary cracks appeared at lower loads than primary cracks in both orientations. Primary crack propagation was found to be preferentially through fine grains in a bimodal microstructure. Grains were aligned and elongated the most towards rolling direction followed by T and S directions resulting in fracture anisotropy. Crystallographic texture and preferential alignment of Ti enriched particles parallel to rolling direction also contributed towards fracture anisotropy.
Directory of Open Access Journals (Sweden)
Roberto Tovo
2016-03-01
Full Text Available This paper reports results of fatigue tests of friction stir welded (FSW aluminium tubes. Relatively small 38 mm diameter tubes were used and hence an automated FSW process using a retracting tool was designed for this project, as the wall thickness of the aluminium tube was similar to the diameter of the FSW tool. This is a more complex joint geometry to weld than the more usual larger diameter tube reported in the literature. S-N fatigue testing was performed using load ratios of R = 0.1 and R = -1. Crack path analysis was performed using both low magnification stereo microscopy and scanning electron microscopy, in order to identify crack initiation sites and to determine the direction of crack propagation. Work is still in progress to follow the crack path through the various microstructural zones associated with the weld. A simple statistical analysis was used to characterize the most typical crack initiation site. This work forms part of a wider project directed at determining multiaxial fatigue design rules for small diameter 6082-T6 aluminium tubes that could be of use in the ground vehicle industry.
Directory of Open Access Journals (Sweden)
J A F O. Correia
2017-10-01
Full Text Available In Portugal there is a number of old metallic riveted railway and highway bridges that were erected by the end of the 19th century and beginning of the 20th century, and are still in operation, requiring inspections and remediation measures to overcome fatigue damage. Residual fatigue life predictions should be based on actual fatigue data from bridge materials which is scarce due to the material specificities. Fatigue crack propagation data of materials from representative Portuguese riveted bridges, namely the Pinh�o and Luiz I road bridges, the Viana road/railway bridge, the F�o road bridge and the Trez�i railway bridge were considered in this study. The fatigue crack growth rates were correlated using the Pariss law. Also, a statistical analysis of the pure mode I fatigue crack growth (FCG data available for the materials from the ancient riveted metallic bridges is presented. Based on this analysis, design FCG curves are proposed and compared with BS7910 standard proposal, for the Paris region, which is one important fatigue regime concerning the application of the Fracture Mechanics approaches, to predict the remnant fatigue life of structural details
Shear-mode Crack Initiation Behavior in the Martensitic and Bainitic Microstructures
Directory of Open Access Journals (Sweden)
Wada Kentaro
2018-01-01
Full Text Available Fully reversed torsional fatigue tests were conducted to elucidate the behaviour of shear-mode crack initiation and propagation in one martensitic and two bainitic steels. The relationship between the crack initiation site and microstructure was investigated by means of an electron backscatter diffraction (EBSD technique. From the S-N diagram, two notable results were obtained: (i the shear-mode crack was initiated on the prior austenitic grain boundary in martensitic steel, while in bainitic steels, the crack was initiated along the {110} plane; one of the slip planes of bcc metals, and (ii the torsional fatigue limit of lower bainitic steel with finer grains was 60 MPa higher than that of upper bainitic steel with coarser grains even though the hardnesses were nearly equivalent. The mechanism determining the torsional fatigue strength in these steels is discussed from the viewpoint of microstructure morphology.
Concrete Cracking Prediction Including the Filling Proportion of Strand Corrosion Products
Wang, Lei; Dai, Lizhao; Zhang, Xuhui; Zhang, Jianren
2016-01-01
The filling of strand corrosion products during concrete crack propagation is investigated experimentally in the present paper. The effects of stirrups on the filling of corrosion products and concrete cracking are clarified. A prediction model of crack width is developed incorporating the filling proportion of corrosion products and the twisting shape of the strand. Experimental data on cracking angle, crack width, and corrosion loss obtained from accelerated corrosion tests of concrete beams are presented. The proposed model is verified by experimental data. Results show that the filling extent of corrosion products varies with crack propagation. The rust filling extent increases with the propagating crack until a critical width. Beyond the critical width, the rust-filling extent remains stable. Using stirrups can decrease the critical crack width. Stirrups can restrict crack propagation and reduce the rust filling. The tangent of the cracking angle increases with increasing corrosion loss. The prediction of corrosion-induced crack is sensitive to the rust-filling extent. PMID:28772367
International Nuclear Information System (INIS)
Gondard, C.
1989-01-01
The results from a study performed on the fatigue crack propagation in PWR vessels are discussed. The purpose of the investigation is to establish a relationship between the length, the place of a defect and the structure's residual life. The tests and the 6 inspections carried out during 5 years are reported. The results show that a defect traversing the structure is expected at the end 1989. The large amount of data allowed a statistical analysis showing the reproductibility of the method [fr
Effect of temperature on the plastic zone in near-threshold fatigue crack propagation in Nb-H alloys
International Nuclear Information System (INIS)
Lin, C.C.; Polvanich, N.; Salama, K.
1987-01-01
The effect of temperature on the formation of plastic zone in near-threshold fatigue crack propagation is investigated in niobium-hydrogen alloys. The study was made with the ultimate goal of determining the role of hydrogen related to test temperatures on the embrittlement and fracture processes of niobium. Fatigue tests were performed at the two temperatures 220 and 350 K on a hydrogen-free specimen as well as specimens containing hydrogen in solid solution and in the form of hydride. Microhardness was measured on the fatigued specimens in order to determine the plastic zone size at positions where the crack propagation was in the near-threshold region. The results show that at both temperatures, the plastic zone size in hydrogen-free niobium decreases as the amount of hydrogen is increased until it reaches a minimum value and then increases as the amount of hydrogen is further increased. The hydrogen concentrations at the minimum plastic zone are found to be approximately equal to those where the maximum embrittlement occurs for each temperature
Energy Technology Data Exchange (ETDEWEB)
Maillot, V
2004-07-01
We studied the behaviour of a 304 L type austenitic stainless steel submitted to thermal fatigue. Using the SPLASH equipment of CEA/SRMA we tested parallelepipedal specimens on two sides: the specimens are continuously heated by Joule effect, while two opposites faces are cyclically. cooled by a mixed spray of distilled water and compressed air. This device allows the reproduction and the study of crack networks similar to those observed in nuclear power plants, on the inner side of circuits fatigued by mixed pressurized water flows at different temperatures. The crack initiation and the network constitution at the surface were observed under different thermal conditions (Tmax = 320 deg C, {delta}T between 125 and 200 deg C). The experiment produced a stress gradient in the specimen, and due to this gradient, the in-depth growth of the cracks finally stopped. The obtained crack networks were studied quantitatively by image analysis, and different parameters were studied: at the surface during the cycling, and post mortem by step-by-step layer removal by grinding. The maximal depth obtained experimentally, 2.5 mm, is relatively coherent with the finite element modelling of the SPLASH test, in which compressive stresses appear at a depth of 2 mm. Some of the crack networks obtained by thermal fatigue were also tested in isothermal fatigue crack growth under 4-point bending, at imposed load. The mechanisms of the crack selection, and the appearance of the dominating crack are described. Compared to the propagation of a single crack, the crack networks delay the propagation, depending on the severity of the crack competition for domination. The dominating crack can be at the network periphery, in that case it is not as shielded by its neighbours as a crack located in the center of the network. It can also be a straight crack surrounded by more sinuous neighbours. Indeed, on sinuous cracks, the loading is not the same all along the crack path, leading to some
International Nuclear Information System (INIS)
Shanmugam, K.; Lakshminarayanan, A.K.; Balasubramanian, V.
2009-01-01
The effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on fatigue crack growth behaviour of the gas tungsten arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single 'V' butt welded joints. Centre cracked tensile (CCT) specimens were prepared to evaluate fatigue crack growth behaviour. Servo hydraulic controlled fatigue testing machine was used to evaluate the fatigue crack growth behaviour of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength, hardness and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.
Comparison of Crack Initiation, Propagation and Coalescence Behavior of Concrete and Rock Materials
Zengin, Enes; Abiddin Erguler, Zeynal
2017-04-01
There are many previously studies carried out to identify crack initiation, propagation and coalescence behavior of different type of rocks. Most of these studies aimed to understand and predict the probable instabilities on different engineering structures such as mining galleries or tunnels. For this purpose, in these studies relatively smaller natural rock and synthetic rock-like models were prepared and then the required laboratory tests were performed to obtain their strength parameters. By using results provided from these models, researchers predicted the rock mass behavior under different conditions. However, in the most of these studies, rock materials and models were considered as contains none or very few discontinuities and structural flaws. It is well known that rock masses naturally are extremely complex with respect to their discontinuities conditions and thus it is sometimes very difficult to understand and model their physical and mechanical behavior. In addition, some vuggy rock materials such as basalts and limestones also contain voids and gaps having various geometric properties. Providing that the failure behavior of these type of rocks controlled by the crack initiation, propagation and coalescence formed from their natural voids and gaps, the effect of these voids and gaps over failure behavior of rocks should be investigated. Intact rocks are generally preferred due to relatively easy side of their homogeneous characteristics in numerical modelling phases. However, it is very hard to extract intact samples from vuggy rocks because of their complex pore sizes and distributions. In this study, the feasibility of concrete samples to model and mimic the failure behavior vuggy rocks was investigated. For this purpose, concrete samples were prepared at a mixture of %65 cement dust and %35 water and their physical and mechanical properties were determined by laboratory experiments. The obtained physical and mechanical properties were used to
Stress corrosion cracking behaviour of Alloy 600 in high temperature water
International Nuclear Information System (INIS)
Webb, G.L.; Burke, M.G.
1995-01-01
The stress corrosion cracking (SCC) susceptibility of Alloy 600 in deaerated water at 360 deg. C, as measured with statistically-loaded U-bend specimens, is dependent upon microstructure and whether the material was cold-worked and annealed (CWA) or hot-worked and annealed (HWA). All cracking was intergranular, and materials lacking grain boundary carbides were most susceptible to SCC initiation. CWA tubing materials are more susceptible to SCC initiation than HWA ring-rolled forging materials with similar microstructures, as determined by light optical metallography (LOM). In CWA tubing materials one crack dominated and grew to a large size that was observable by visual inspection. HWA materials with a low hot-working finishing temperature (below 925 deg. C) and final anneals at temperatures ranging from 1010 deg. C to 1065 deg. C developed both large cracks, similar to those found in CWA materials, and also small intergranular microcracks, which are detectable only by destructive metallographic examination. HWA materials with a high hot-working finishing temperature (above 980 deg. C) and high-temperature final anneal (above 1040 deg. C), with grain boundaries that are fully decorated, developed only microcracks, which were observed in all specimens examined. These materials developed no large, visually detectable cracks, even after more than 300 weeks exposure. A low-temperature thermal treatment (610 deg. C for 7h), which reduced or eliminates SCC in Alloy 600, did not eliminate microcrack formation in the high temperature processed HWA materials. Detailed microstructural characterization using conventional metallographic and analytical electron microscopy (AEM) techniques was performed on selected materials to identify the factors responsible for the observed differences in cracking behaviour. 11 refs, 12 figs, 3 tabs
Transient cracks and triple junctions induced by Cocos-Nazca propagating rift
Schouten, H.; Smith, D. K.; Zhu, W.; Montesi, L. G.; Mitchell, G. A.; Cann, J. R.
2009-12-01
The Galapagos triple junction is a ridge-ridge-ridge triple junction where the Cocos, Nazca, and Pacific plates meet around the Galapagos microplate (GMP). On the Cocos plate, north of the large gore that marks the propagating Cocos-Nazca (C-N) Rift, a 250-km-long and 50-km-wide band of NW-SE-trending cracks crosscuts the N-S-trending abyssal hills of the East Pacific Rise (EPR). These appear as a succession of minor rifts, accommodating some NE-SW extension of EPR-generated seafloor. The rifts successively intersected the EPR in triple junctions at distances of 50-100 km north of the tip of the C-N Rift. We proposed a simple crack interaction model to explain the location of the transient rifts and their junction with the EPR. The model predicts that crack locations are controlled by the stress perturbation along the EPR, induced by the dominant C-N Rift, and scaled by the distance of its tip to the EPR (Schouten et al., 2008). The model also predicts that tensile stresses are symmetric about the C-N Rift and thus, similar cracks should have occurred south of the C-N Rift prior to formation of the GMP about 1 Ma. There were no data at the time to test this prediction. In early 2009 (AT 15-41), we mapped an area on the Nazca plate south of the C-N rift out to 4 Ma. The new bathymetric data confirm the existence of a distinctive pattern of cracks south of the southern C-N gore that mirrors the pattern on the Cocos plate until about 1 Ma, and lends support to the crack interaction model. The envelope of the symmetric cracking pattern indicates that the distance between the C-N Rift tip and the EPR varied between 40 and 65 km during this time (1-4 Ma). The breakdown of the symmetry at 1 Ma accurately dates the onset of a southern plate boundary of the GMP, now Dietz Deep Rift. At present, the southern rift boundary of the GMP joins the EPR with a steep-sided, 80 km long ridge. This ridge releases the stress perturbation otherwise induced along the EPR by elastic
International Nuclear Information System (INIS)
Serres, A.
2008-01-01
During the PWR power transients, iodine-induced stress corrosion cracking (I-SCC) is one of the potential failure modes of Zircaloy-4 fuel claddings under Pellet-Cladding Interaction conditions. The primary objective of this study is to distinguish the parameters that contribute to the I-SCC phenomenon in iodized methanol solutions at ambient temperature, on notched tensile specimens, using crack growth rate measurements provided by Direct Current Potential Drop. The results show that for a KI lower than 20 MPa.m 1/2 , the IG and mixed IG/TG velocity of propagation is a linear function of KI, regardless of the propagation mode. Between 20 and 25 MPa.m 1/2 , the TG crack growth rate also depends linearly on KI, but increases at a faster rate with respect to KI than during the IG and mixed IG/TG propagation steps. The crack propagation direction and plane (LT and TL) have an impact on the propagation modes, but no impact on the kinetics. The increase of iodine content induces an increase of the crack growth rate for a given KI, and a decrease of the KI, threshold, allowing the crack propagation. This work enables us to quantify the effect of iodine content and of KI on the crack propagation step, propose a propagation law taking into accounts these parameters, and improve the I-SCC description for models. During operation, a zirconium cladding is neutron-irradiated, modifying its microstructure and deformation modes. The second objective of the study is therefore to investigate the impact of these modifications on I-SCC. For that purpose, smooth specimens in recrystallized Zircaloy-4 are proton-irradiated to 2 dpa at 305 C, the microstructure and deformation modes of unirradiated and irradiated Zircaloy-4 are characterized by TEM and SEM, and the influence of these radiation-induced modifications on the I-SCC susceptibility is studied. The Laves phases precipitates are slightly modified by irradiation. The formation of P -type dislocation loops correlated with
International Nuclear Information System (INIS)
Le Delliou, P.; Hornet, P.
2001-01-01
This paper presents some work conducted at EDF R and D Division to evaluate the probability that a semi-elliptical crack in a pipe not only initiates but also propagates when submitted to mechanical loading such as bending and pressure combined or not with a thermal shock. The first part is related to the description of the mechanical model: the simplified methods included in the French RSE-M Code used to evaluate the J-integral as well as the principle of the determination of the crack propagation. Then, the way this deterministic approach is combined to a reliability code is described. Finally, an example is shown: the initiation and the instability of a semi-elliptical crack in a pipe submitted to combined pressure and bending moment. (author)
International Nuclear Information System (INIS)
James, L.A.
1987-01-01
The fatigue-crack propagation (FCP) behavior of ASTM A533-B-1 steel was characterized in vacuo at 288 0 C. Tests were conducted at two stress ratios: R = 0.05 and R = 0.7. Results of these tests were compared with results from previous studies for the same type of steel tested in an air environment, and FCP rates in vacuo were generally lower than those in air. Stress ratio effects in vacuo were not as great as those in air, and both stress ratio effects and environmental effects are discussed from the standpoint of crack closure concepts
Fatigue crack growth in mode II of adhesively joined composites
DEFF Research Database (Denmark)
Biel, Anders; Toftegaard, Helmuth Langmaack
2017-01-01
, experiments are performed to derive material data for a crack propagation in shear i.e. in mode II. The shear loading of the crack is achieved by use of double cantilever beam specimens loaded with uneven bending moments. The experiments are performed under a constant cyclic displacement. An initial mode I...... loading is used to make the crack start in the adhesive. The crack length is measured using a load synchronized camera. Due to the shear loading the crack deviates from the adhesive layer into the laminate. A stable crack propagation is detected in the laminate. No influence have been detected due...... to an increasing crack length. It is also observed that the crack is trapped in the laminate; if the loading is changed to mode I the crack continues to propagate in the laminate....
Grain by grain study of the mechanisms of crack propagation during iodine SCC of Zry-4
International Nuclear Information System (INIS)
Haddad Andalag, R.E.
1993-01-01
This paper describes the tests conducted to determine the conditions leading to cracking of a specified grain of metal, focussing on the crystallographic orientation of crack paths, the critical stress conditions and the significance of the fractographic features encountered. In order to get orientable cracking, a technique was developed to produce iodine SCC, by means of pressurizing tubes of a specially heat treated Zry-4 having very large grains, shaped as discs of a few millimeters in diameter and grown up to the wall thickness. Careful orientation of fractured grains, performed by means of a back-reflection Laue technique with a precision better than one degree, has proved that transgranular cracking occurs only along basal planes. The effect of anisotropy, plasticity, triaxiality and residual stresses originated in thermal contraction, has to be considered to account for the influence of the stress state . A grain by grain calculation led to the conclusion that transgranular cracking always occurs on those bearing the maximum resolved tensile stress on basal planes. There are clear indications of the need of a triaxial stress state for the process to occur. Fracture modes other than pseudo-cleavage have been encountered, including intergranular separation, ductile tearing produced by prismatic slip and propagation along twin boundaries. In each case the fractographic features have been identified, and associations have been made with fractographs obtained in normal fuel cladding. (Author)
Influence of dissolved hydrogen on the fatigue crack growth behaviour of AISI 4140 steel
Ramasagara Nagarajan, Varun
Many metallic structural components come into contact with hydrogen during manufacturing processes or forming operations such as hot stamping of auto body frames and while in service. This interaction of metallic parts with hydrogen can occur due to various reasons such as water molecule dissociation during plating operations, interaction with atmospheric hydrogen due to the moisture present in air during stamping operations or due to prevailing conditions in service (e.g.: acidic or marine environments). Hydrogen, being much smaller in size compared to other metallic elements such as Iron in steels, can enter the material and become dissolved in the matrix. It can lodge itself in interstitials locations of the metal atoms, at vacancies or dislocations in the metallic matrix or at grain boundaries or inclusions (impurities) in the alloy. This dissolved hydrogen can affect the functional life of these structural components leading to catastrophic failures in mission critical applications resulting in loss of lives and structural component. Therefore, it is very important to understand the influence of the dissolved hydrogen on the failure of these structural materials due to cyclic loading (fatigue). For the next generation of hydrogen based fuel cell vehicles and energy systems, it is very crucial to develop structural materials for hydrogen storage and containment which are highly resistant to hydrogen embrittlement. These materials should also be able to provide good long term life in cyclic loading, without undergoing degradation, even when exposed to hydrogen rich environments for extended periods of time. The primary focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behaviour of a commercially available high strength medium carbon low alloy (AISI 4140) steel. The secondary objective was to examine the influence of microstructure on the fatigue crack growth behaviour of this material and to determine the
Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD
Energy Technology Data Exchange (ETDEWEB)
Laureys, A., E-mail: Aurelie.Laureys@UGent.be [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Depover, T. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Petrov, R. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Verbeken, K. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium)
2016-02-15
The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses just after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of
Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD
International Nuclear Information System (INIS)
Laureys, A.; Depover, T.; Petrov, R.; Verbeken, K.
2016-01-01
The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses just after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of
Hole Defects Affect the Dynamic Fracture Behavior of Nearby Running Cracks
Directory of Open Access Journals (Sweden)
R. S. Yang
2018-01-01
Full Text Available Effects of defects on the dynamic fracture behavior of engineering materials cannot be neglected. Using the experimental system of digital laser dynamic caustics, the effects of defects on the dynamic fracture behavior of nearby running cracks are studied. When running cracks propagate near to defects, the crack path deflects toward the defect; the degree of deflection is greater for larger defect diameters. When the running crack propagates away from the defect, the degree of deflection gradually reduces and the original crack path is restored. The intersection between the caustic spot and the defect is the direct cause of the running crack deflection; the intersection area determines the degree of deflection. In addition, the defect locally inhibits the dynamic stress intensity factor of running cracks when they propagate toward the defect and locally promotes the dynamic stress intensity factor of running cracks when they propagate away from the defect.
Fatigue crack behaviour in mine excavator
Energy Technology Data Exchange (ETDEWEB)
Yin, Y.; Grondin, G.Y.; Elwi, A.E. [Alberta Univ., Edmonton, AB (Canada). Dept. of Civil and Environmental Engineering
2006-05-15
Fatigue cracking in excavation equipment represents a significant operating cost for oil sands operators. It is caused by high impact loads, the high frequency of load cycles, and large component sizes found in oil sands processing facilities. Monitoring and repair strategies for fatigue cracks are typically based on vendor specifications and the experience of maintenance personnel. This paper provided details of an optimized crack management program applied to a BE 395B shovel boom. The proposed crack management tool uses a chart to predict the remaining life of a corner crack in the shovel boom. Predictions are based on limited field measurements of operating loads as well as on data obtained from fatigue testing of boom material, and a finite element analysis of the shovel boom. Field and laboratory data are used along with fracture mechanics and finite element modelling to predict crack life. It was concluded that the tool will allow inspectors and planners to schedule repairs based on safe service life. The tool is applicable for any components subjected to fatigue loading. 3 refs., 21 tabs., 64 figs.
Energy Technology Data Exchange (ETDEWEB)
Kubo, T., E-mail: kubo@nfd.co.jp [Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Ibaraki 311-1313 (Japan); Kobayashi, Y. [M.O.X. Co., Ltd., 1828-520 Hirasu-cho, Mito, Ibaraki 311-0853 (Japan)
2013-08-15
Highlights: • Steady state crack velocity of delayed hydride cracking in Zircaloy-2 was analyzed. • A large stress peak is induced at an end of hydride by volume expansion of hydride. • Hydrogen diffuses to the stress peak, thereby accelerating steady hydride growth. • Crack velocity was estimated from the calculated hydrogen flux into the stress peak. • There was good agreement between calculation results and experimental data. -- Abstract: Delayed hydride cracking (DHC) of Zircaloy-2 is one possible mechanism for the failure of boiling water reactor fuel rods in ramp tests at high burnup. Analyses were made for hydrogen diffusion around a crack tip to estimate the crack velocity of DHC in zirconium alloys, placing importance on effects of precipitation of δ-hydride. The stress distribution around the crack tip is significantly altered by precipitation of hydride, which was strictly analyzed using a finite element computer code. Then, stress-driven hydrogen diffusion under the altered stress distribution was analyzed by a differential method. Overlapping of external stress and hydride precipitation at a crack tip induces two stress peaks; one at a crack tip and the other at the front end of the hydride precipitate. Since the latter is larger than the former, more hydrogen diffuses to the front end of the hydride precipitate, thereby accelerating hydride growth compared with that in the absence of the hydride. These results indicated that, after hydride was formed in front of the crack tip, it grew almost steadily accompanying the interaction of hydrogen diffusion, hydride growth and the stress alteration by hydride precipitation. Finally, crack velocity was estimated from the calculated hydrogen flux into the crack tip as a function of temperature, stress intensity factor and material strength. There was qualitatively good agreement between calculation results and experimental data.
Rovinelli, Andrea; Sangid, Michael D.; Proudhon, Henry; Guilhem, Yoann; Lebensohn, Ricardo A.; Ludwig, Wolfgang
2018-06-01
Small crack propagation accounts for most of the fatigue life of engineering structures subject to high cycle fatigue loading conditions. Determining the fatigue crack growth rate of small cracks propagating into polycrystalline engineering alloys is critical to improving fatigue life predictions, thus lowering cost and increasing safety. In this work, cycle-by-cycle data of a small crack propagating in a beta metastable titanium alloy is available via phase and diffraction contrast tomography. Crystal plasticity simulations are used to supplement experimental data regarding the micromechanical fields ahead of the crack tip. Experimental and numerical results are combined into a multimodal dataset and sampled utilizing a non-local data mining procedure. Furthermore, to capture the propensity of body-centered cubic metals to deform according to the pencil-glide model, a non-local driving force is postulated. The proposed driving force serves as the basis to construct a data-driven probabilistic crack propagation framework using Bayesian networks as building blocks. The spatial correlation between the postulated driving force and experimental observations is obtained by analyzing the results of the proposed framework. Results show that the above correlation increases proportionally to the distance from the crack front until the edge of the plastic zone. Moreover, the predictions of the propagation framework show good agreement with experimental observations. Finally, we studied the interaction of a small crack with grain boundaries (GBs) utilizing various slip transmission criteria, revealing the tendency of a crack to cross a GB by propagating along the slip directions minimizing the residual Burgers vector within the GB.
Effects of temperature on SCC propagation in high temperature water injected with hydrogen peroxide
International Nuclear Information System (INIS)
Nakano, Junichi; Sato, Tomonori; Kato, Chiaki; Yoshiyuki, Kaji; Yamamoto, Masahiro; Tsukada, Takashi
2012-09-01
To understand the stress corrosion cracking (SCC) behaviour of austenitic stainless steels (SSs) in the boiling water reactor (BWR) coolant environment, it is significant to investigate the effect of hydrogen peroxide (H 2 O 2 ) produced by the radiolysis of water on SCC under the various water chemistry and operational conditions. At the start-up or shut-down periods, for example, the conditions of radiation and temperature on the structural materials are different from those during the plant normal operation, and may be influencing on SCC behaviour. Therefore, the effect of temperature on SCC in high temperature water injected with H 2 O 2 was evaluated by SCC propagation test at the present study. Oxide films on the metal surface in crack were examined and the thermal equilibrium diagram was calculated to estimate the environmental situation in the crack. On the thermally sensitized type 304 SS, crack growth tests were conducted in high temperature water injected with H 2 O 2 to simulate water radiolysis in the core. Small CT type specimens with a width of 15.5 mm and thickness of 6.2 mm were machined from the sensitized SS. SCC growth tests were conducted in high temperature water injected with 100 ppb H 2 O 2 at 453 and 561 K. To minimize H 2 O 2 decomposition by a contact with metal surface of autoclave, the CT specimen was isolated from inner surface of the autoclave by the inner modules made of polytetrafluoroethylene (PTFE), and PTFE lining was also used for the inner surface of inlet and sampling tubes. Base on the measurement of sampled water, it was confirmed that 80-90 % of injected H 2 O 2 remained around the CT specimen in autoclave. Constant load at initial K levels of 11-20 MPam 1/2 was applied to the CT specimens during crack growth tests. After crack growth tests, CT specimens were split into two pieces on the plane of crack propagation. Scanning electron microscope (SEM) examination and laser Raman spectroscopy for outer oxide layer of oxide
Crack Front Segmentation and Facet Coarsening in Mixed-Mode Fracture
Chen, Chih-Hung; Cambonie, Tristan; Lazarus, Veronique; Nicoli, Matteo; Pons, Antonio J.; Karma, Alain
2015-12-01
A planar crack generically segments into an array of "daughter cracks" shaped as tilted facets when loaded with both a tensile stress normal to the crack plane (mode I) and a shear stress parallel to the crack front (mode III). We investigate facet propagation and coarsening using in situ microscopy observations of fracture surfaces at different stages of quasistatic mixed-mode crack propagation and phase-field simulations. The results demonstrate that the bifurcation from propagating a planar to segmented crack front is strongly subcritical, reconciling previous theoretical predictions of linear stability analysis with experimental observations. They further show that facet coarsening is a self-similar process driven by a spatial period-doubling instability of facet arrays.
Fatigue-crack propagation behavior of Inconel 718
International Nuclear Information System (INIS)
James, L.A.
1975-09-01
The techniques of linear-elastic fracture mechanics were used to characterize the effect of several variables (temperature, environment, cyclic frequency, stress ratio, and heat-treatment variations) upon the fatigue-crack growth behavior of Inconel 718 base metal and weldments. Relevant crack growth data on this alloy from other laboratories is also presented. (33 fig, 39 references)
DEFF Research Database (Denmark)
Martakos, G.; Andreasen, J. H.; Berggreen, Christian
2017-01-01
A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect o...
Energy Technology Data Exchange (ETDEWEB)
Raquet, O
1994-11-25
A purely phenomenological study of stress corrosion cracking was performed using the couple Z2CN 18.10 (304L) austenitic stainless steel/boiling MgCl{sub 2} aqueous solution. The exploitation of the morphological information (shape of the cracks and size distribution) available after constant elongation rate tests led to the proposal of an analytical expression of the crack initiation and growth rates. This representation allowed to quantitatively characterize the influence of the applied strain rate as well as the effect of corrosion inhibitors on the crack initiation and propagation phases. It can be used in the search for the stress corrosion cracking mechanisms as a `riddle` for the determination of the rate controlling steps. As a matter of fact, no mechanistic hypothesis has been used for its development. (author).
Statistical distribution of time to crack initiation and initial crack size using service data
Heller, R. A.; Yang, J. N.
1977-01-01
Crack growth inspection data gathered during the service life of the C-130 Hercules airplane were used in conjunction with a crack propagation rule to estimate the distribution of crack initiation times and of initial crack sizes. A Bayesian statistical approach was used to calculate the fraction of undetected initiation times as a function of the inspection time and the reliability of the inspection procedure used.
International Nuclear Information System (INIS)
Tohgo, Keiichiro; Suzuki, Hiromitsu; Shimamura, Yoshinobu; Nakayama, Guen; Hirano, Takashi
2008-01-01
Stress corrosion cracking (SCC) in structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack propagation and multiple large crack formation or final failure under the combination of materials, stress and corrosive environment. In this paper, a Monte Carlo simulation for the process of SCC has been proposed based on the stochastic properties of micro crack initiation and fracture mechanics concept for crack coalescence and propagation. The emphasis in the model is put on the influence of semi-elliptical surface cracks. Numerical simulations are carried out based on CBB (creviced bent beam) test results of a sensitized stainless steel SUS 304 and the influence of micro crack initiation rate and coalescence condition on the simulation results is discussed. The numerical examples indicate the applicability of the present model to a prediction of the SCC behavior in real structures. (author)
Fatigue crack growth in welded joints in seawater
Energy Technology Data Exchange (ETDEWEB)
Lambert, S.B.
1988-01-01
A pipe-to-plate specimen has been developed to study the influence of seawater on the fatigue behaviour of welded tubular joints. DC potential drop techniques have been used to detect fatigue crack initiation, and to monitor the subsequent growth of fatigue cracks. Results for three specimens, tested in air are compared with similar data for tubular and T-plate joints. These comparisons indicate that the pipe/plate is a reasonable model of a tubular joint. Testing was performed on a further six specimens in artificial seawater; two each with free corrosion, optimum cathodic protection, and cathodic overprotection. Fatigue life reduction factors compared with corresponding tests in air were 1.8 and 2.8 for free corrosion, 1.7 and 1.1 with cathodic protection, and 4.2 and 3.3 with cathodic over-protection. These fatigue life reduction factors were comparable to results on T-plate specimens, and were strongly dependent on crack shape development. Linear elastic fracture mechanics techniques appear suitable for the calculation of fatigue crack propagation life. Three approximate solution techniques for crack tip stress intensity factors show reasonable agreement with experimentally derived values. It is recommended that forcing functions be used to model crack aspect ratio development in welded joints. Such forcing functions are influenced by the initial stress distribution and the environment. 207 refs., 192 figs., 22 tabs.
On short cracks that depart from elastoplastic notch tips
Directory of Open Access Journals (Sweden)
Verônica Miquelin Machado
2017-07-01
Full Text Available The behavior of short cracks that depart from elastoplastic notch tips is modeled to estimate the stresses required to initiate and to propagate cracks in notched structural components, and to evaluate the size of tolerable crack-like defects under general loading conditions. This analysis can model both fatigue and environmentally assisted cracking problems; can evaluate notch sensitivity in both cases; and can as well be used to establish design or acceptance criteria for tolerable non-propagating crack-like defects in such cases. The growth of short cracks is assumed driven by the applied stresses and by the stress gradient ahead the notch tip, and supported by the material resistances to crack initiation and to long crack propagation by fatigue or EAC. In the elastoplastic case, the stress gradient ahead of the notch tip is quantified by a J-field to consider the short crack behavior. The tolerable short crack predictions made by this model are evaluated by suitable fatigue and EAC tests of notched specimens specially designed to start nonpropagating cracks from the notch tips, both under elastic and elastoplastic conditions.
International Nuclear Information System (INIS)
Varma, V.K.; Saxena, V.K.; Srinivas, M.
1993-01-01
A model has been developed in the recent past to predict fatigue crack growth (FCG) behaviour in the Paris-regime of various steels by employing low cycle fatigue (LCF) properties. The model forms its basis on the assumption that the cyclic damage process immediately ahead of a crack-tip, restricted in a small zone termed as process zone, is identical to those experienced in the LCF loading of a smooth specimen. Within the process zone, fatigue damage has been assumed in terms of product of stress and plastic strain which is analogous to the plastic strain energy density of the smooth specimen under fatigue loading. In this paper the model developed by Kujawski and Ellyin has been used to predict the FCG behaviour of an α-β titanium alloy in the Paris-regime by employing the experimentally obtained LCF properties. The FCG behaviour thus theoretically predicted was compared with the experimentally determined FCG behaviour
Surface crack growth in cylindrical hollow specimen subject to tension and torsion
Directory of Open Access Journals (Sweden)
V. Shlyannikov
2015-07-01
Full Text Available The subject for studies is an aluminium cylindrical hollow specimen with external axial and part circumferential semi-elliptical surface crack undergoing fatigue loads. Both the optical microscope measurements and the crack opening displacement (COD method are used to monitor and calculate both crack depth and crack length during the tests. The variation of crack growth behaviour is studied under cyclic axial tension, pure torsion and combined tension+torsion fatigue loading. For the particular surface flaw geometries considered, the elastic and plastic in-plane and out-of-plane constraint parameters, as well as the governing parameter for stress fields in the form of In-integral and plastic stress intensity factor, are obtained as a function of the aspect ratio, dimensionless crack length and crack depth. The combined effect of tension and torsion loading and initial surface flaw orientation on the crack growth for two type of aluminium alloys is made explicit. The experimental and numerical results of the present study provided the opportunity to explore the suggestion that fatigue crack propagation may be governed more strongly by the plastic stress intensity factor rather than the magnitude of the elastic SIFs alone. One advantage of the plastic SIF is its sensitivity to combined loading due to accounting for the plastic properties of the material.
Directory of Open Access Journals (Sweden)
Gourdin Cédric
2018-01-01
Full Text Available The integrity of structures exhibiting flaws in Pressurized Water Reactor (PWR has to be assessed to meet safety criteria. This paper deals with crack-propagation under cyclic thermo-mechanical loadings, as encountered in class I austenitic pipes of PWR’s. To have a conservative and reliable assessment of the crack propagation due to the in-service loading, various codes and standards use simplified method. For example, the RSE-M Code introduces a plastic correction depending on the proportion of the mechanical loading. An improvement of the current method requires additional investigations. Moreover, components loaded with transient or thermal fluctuations are not really in loadcontrolled conditions. To this end, a device called PROFATH was designed. The specimen is a pre-cracked thick-walled tube undergoing a set of thermal cycles and loaded with a static mechanical force. During the first part of the thermal cycle, a high frequency induction coil heats the external wall of the tube. Then, the heating system stops and the specimen is cooled down by running water inside the tube. Finite element calculations show that only a region half-way along the tube should be heated to ensure adequate structural effect. In the heated zone, the machining of a sharp circumferential groove ensures the propagation of a unique crack. An electro-mechanical jack controls the level of the mechanical static load. Tests have been carried out, and these tests allow having an evaluation of the pertinence of the correction proposed by the RSE-M Code for a significant plasticity.
International RILEM Workshop on Creep Behaviour in Cracked Sections of Fibre Reinforced Concrete
Llano-Torre, Aitor; Cavalaro, Sergio
2017-01-01
This is the first publication ever focusing strictly on the creep behaviour in cracked sections of Fibre Reinforced Concrete (FRC). These proceedings contain the latest scientific papers about new testing methodologies, results and conclusions of multiple experimental campaigns and recommendations about significant factors of long-term behaviour, experiences from more than ten years of creep testing and some reflections about future perspectives on this topic. This book is an essential reference for all researchers of creep behaviour on FRC. This volume is the result of the efforts of the RILEM TC 261-CCF, that has been working since 2014 to develop standardized methodologies and guidelines to compare results from different laboratories and get a better understanding of the significant parameters related to creep of FRC.
Stress corrosion and corrosion fatigue crack growth monitoring in metals
International Nuclear Information System (INIS)
Senadheera, T.; Shipilov, S.A.
2003-01-01
Environmentally assisted cracking (including stress corrosion cracking and corrosion fatigue) is one of the major causes for materials failure in a wide variety of industries. It is extremely important to understand the mechanism(s) of environmentally assisted crack propagation in structural materials so as to choose correctly from among the various possibilities-alloying elements, heat treatment of steels, parameters of cathodic protection, and inhibitors-to prevent in-service failures due to stress corrosion cracking and corrosion fatigue. An important step towards understanding the mechanism of environmentally assisted crack propagation is designing a testing machine for crack growth monitoring and that simultaneously provides measurement of electrochemical parameters. In the present paper, a direct current (DC) potential drop method for monitoring crack propagation in metals and a testing machine that uses this method and allows for measuring electrochemical parameters during stress corrosion and corrosion fatigue crack growth are described. (author)
International Nuclear Information System (INIS)
Ohnami, M.; Sakane, M.; Nishino, S.
1987-01-01
The following two series of studies are described: One is crack propagation life prediction in high-temperature low-cycle fatigue tests under triangular and trapezoidal strain or stress waves for austenitic stainless steel by X-ray fractography. Another is remaining life prediction of the steel under creep-fatigue interacted conditions by applying the concept of the remaining life diagram and X-ray profile analysis. Particle size and microstrain obtained by X-ray profile analysis were effective nondestructive parameters for estimating crack propagation life and remaining life in creep-fatigue interaction
Handa, Danish; Sekhar Dondapati, Raja; Kumar, Abhinav
2017-08-01
Ductile to brittle transition (DTBT) is extensively observed in materials under cryogenic temperatures, thereby observing brittle failure due to the non-resistance of crack propagation. Owing to its outstanding mechanical and thermal properties, Kevlar 49 composites are widely used in aerospace applications under cryogenic temperatures. Therefore, in this paper, involving the assumption of linear elastic fracture mechanics (LEFM), mechanical characterization of Kevlar 49 composite is done using Extended Finite Element Method (X-FEM) technique in Abaqus/CAE software. Further, the failure of Kevlar 49 composites due to the propagation of crack at room temperature and the cryogenic temperature is investigated. Stress, strain and strain energy density as a function of the width of the Kevlar specimen is predicted, indicates that Kevlar 49 composites are suitable for use under cryogenic temperatures.
On the role of weak interface in crack blunting process in nanoscale layered composites
Li, Yi; Zhou, Qing; Zhang, Shuang; Huang, Ping; Xu, Kewei; Wang, Fei; Lu, Tianjian
2018-03-01
Heterointerface in a nanoscale metallic layered composite could improve its crack resistance. However, the influence of metallic interface structures on crack propagation has not been well understood at atomic scale. By using the method of molecular dynamics (MD) simulation, the crack propagation behavior in Cu-Nb bilayer is compared with that in Cu-Ni bilayer. We find that the weak Cu-Nb interface plays an important role in hindering crack propagation in two ways: (i) dislocation nucleation at the interface releases stress concentration for the crack to propagate; (ii) the easily sheared weak incoherent interface blunts the crack tip. The results are helpful for understanding the interface structure dependent crack resistance of nanoscale bicrystal interfaces.
Ductile crack growth simulation from near crack tip dissipated energy
International Nuclear Information System (INIS)
Marie, S.; Chapuliot, S.
2000-01-01
A method to calculate ductile tearing in both small scale fracture mechanics specimens and cracked components is presented. This method is based on an estimation of the dissipated energy calculated near the crack tip. Firstly, the method is presented. It is shown that a characteristic parameter G fr can be obtained, relevant to the dissipated energy in the fracture process. The application of the method to the calculation of side grooved crack tip (CT) specimens of different sizes is examined. The value of G fr is identified by comparing the calculated and experimental load line displacement versus crack extension curve for the smallest CT specimen. With this identified value, it is possible to calculate the global behaviour of the largest specimen. The method is then applied to the calculation of a pipe containing a through-wall thickness crack subjected to a bending moment. This pipe is made of the same material as the CT specimens. It is shown that it is possible to simulate the global behaviour of the structure including the prediction of up to 90-mm crack extension. Local terms such as the equivalent stress or the crack tip opening angle are found to be constant during the crack extension process. This supports the view that G fr controls the fields in the vicinity near the crack tip. (orig.)
Effect of overload on the fatigue crack propagation in metastable beta Ti-V alloys
International Nuclear Information System (INIS)
Chakrabortty, S.B.; Starke, E.A. Jr.; Lee, E.W.
1984-01-01
The effects of overload on the fatigue crack propagation behavior of two Ti-V alloys having different deformation mechanisms were studied. The results are explained in terms of residual stress effects associated with the overload and the removal of these stresses during post-overload cycling. An additional effect occurs during multiple cycle overload when the deformation structure representative of the strain amplitude is believed to form in the overload reverse plastic zone. This structure must be rearranged during cycling at Delta Kb before the baseline FCGR is reached and the process is responsible for part of the delay period. 46 references
Brittle versus ductile behaviour of nanotwinned copper: A molecular dynamics study
International Nuclear Information System (INIS)
Pei, Linqing; Lu, Cheng; Zhao, Xing; Zhang, Liang; Cheng, Kuiyu; Michal, Guillaume; Tieu, Kiet
2015-01-01
Nanotwinned copper (Cu) exhibits an unusual combination of ultra-high yield strength and high ductility. A brittle-to-ductile transition was previously experimentally observed in nanotwinned Cu despite Cu being an intrinsically ductile metal. However, the atomic mechanisms responsible for brittle fracture and ductile fracture in nanotwinned Cu are still not clear. In this study, molecular dynamics (MD) simulations at different temperatures have been performed to investigate the fracture behaviour of a nanotwinned Cu specimen with a single-edge-notched crack whose surface coincides with a twin boundary. Three temperature ranges are identified, indicative of distinct fracture regimes, under tensile straining perpendicular to the twin boundary. Below 1.1 K, the crack propagates in a brittle fashion. Between 2 K and 30 K a dynamic brittle-to-ductile transition is observed. Above 40 K the crack propagates in a ductile mode. A detailed analysis has been carried out to understand the atomic fracture mechanism in each fracture regime
On the application of cohesive crack modeling in cementitious materials
DEFF Research Database (Denmark)
Stang, Henrik; Olesen, John Forbes; Poulsen, Peter Noe
2007-01-01
typically for multi scale problems such as crack propagation in fiber reinforced composites. Mortar and concrete, however, are multi-scale materials and the question naturally arises, if bridged crack models in fact are more suitable for concrete and mortar as well? In trying to answer this question a model......Cohesive crack models-in particular the Fictitious Crack Model - are applied routinely in the analysis of crack propagation in concrete and mortar. Bridged crack models-where cohesive stresses are assumed to exist together with a stress singularity at the crack tip-on the other hand, are used...
Modelling of cracking and inelastic behaviour of reinforced concrete structures
International Nuclear Information System (INIS)
Young, A.G.; Albana, M.O.
1989-09-01
The report contains a review of work available in the literature on local bond transfer and the main factors which influence it, involving deformed reinfocing bar. Possible load transfer mechanisms are investigated and the significance of secondary cracking, local consolidation and shearing assessed. On the basis of these studies a linkage element which realistically models bond action, and is applicable to both monotonic and cyclic load, is proposed. Its ability to accurately predict stress, strain and crack geometry in typical reinforced concrete components is demonstrated by comparison of the results of finite element analysis using this model with experimental data. Aspects requiring further research are identified. An analysis of the dynamic response of a reinforced concrete beam is given which makes the simplifying assumption of rigid-plastic behaviour. A comparison of the analytical solution with experimental results obtained by bend tests in the Large Dynamic Test Facility at Ispra shows that, despite the neglect of elastic vibrations, a reasonable prediction of the fundamental response is obtained providing due allowance is made for rate-of-strain effects
Near-IR imaging of cracks in teeth
Fried, William A.; Simon, Jacob C.; Lucas, Seth; Chan, Kenneth H.; Darling, Cynthia L.; Staninec, Michal; Fried, Daniel
2014-02-01
Dental enamel is highly transparent at near-IR wavelengths and several studies have shown that these wavelengths are well suited for optical transillumination for the detection and imaging of tooth decay. We hypothesize that these wavelengths are also well suited for imaging cracks in teeth. Extracted teeth with suspected cracks were imaged at several wavelengths in the near-IR from 1300-1700-nm. Extracted teeth were also examined with optical coherence tomography to confirm the existence of suspected cracks. Several teeth of volunteers were also imaged in vivo at 1300-nm to demonstrate clinical potential. In addition we induced cracks in teeth using a carbon dioxide laser and imaged crack formation and propagation in real time using near-IR transillumination. Cracks were clearly visible using near-IR imaging at 1300-nm in both in vitro and in vivo images. Cracks and fractures also interfered with light propagation in the tooth aiding in crack identification and assessment of depth and severity.
Miniaturized fatigue crack growth specimen technology and results
International Nuclear Information System (INIS)
Puigh, R.J.; Bauer, R.E.; Ermi, A.M.; Chin, B.A.
1981-01-01
The miniature fatigue crack propagation technology has been extended to in-cell fabrication of irradiated specimens. Baseline testing of selected titanium alloys has been performed at 25 0 C in air. At relatively small values for the stress intensity factor, ΔK, the crack growth rates for all titanium alloys investigated are within a factor of three. The crack growth rates for these titanium alloys are a factor of three greater than the crack growth rates of either 316SS (20% CW) or HT-9. Each of the titanium alloys has observable crack propagation for stress intensity factors as small as 4.2 MPa√m
Study on crack propagation of adhesively bonded DCB for aluminum foam using energy release rate
Energy Technology Data Exchange (ETDEWEB)
Bang, Hye Jin; Lee, Sang Kyo; Cho, Chong Du [Inha University, Incheon (Korea, Republic of); Cho, Jae Ung [Kongju National University, Choenan (Korea, Republic of)
2015-01-15
Aluminum foam with initial crack, which has a closed cell form adhesively bonded, is studied to compare and analyze the crack propagation behavior by using both experimental and finite element analysis techniques. The specimen is loaded in Mode I type of fracture as 15 mm/min speed of a displacement control method. The experimental results were used to accommodate the finite element analysis performed with commercial software ABAQUS 6.10. First, using a video recording, five steps of experiment were selected at random and then the energy release rate was calculated. The estimated energy release rate was then used as fracture energy into the finite element analysis. Comparing the experimental axial load-displacement graphs and the finite element analysis results, roughly equivalent peak values were observed in the cohesive strength of the aluminum foam double cantilever beam. However, force versus displacement patterns showed somewhat different: little deformation was observed in aluminum foam, whereas adhesive parts in double cantilever beam were significantly deformed.
Directory of Open Access Journals (Sweden)
Filippo Berto
2016-10-01
Full Text Available The torsional fatigue behaviour of circumferentially notched specimens made of austenitic stainless steel, SUS316L, and carbon steel, SGV410, characterized by different notch root radii has been recently investigated by Tanaka. In that contribution, it was observed that the total fatigue life of the austenitic stainless steel increases with increasing stress concentration factor for a given applied nominal shear stress amplitude. By using the electrical potential drop method, Tanaka observed that the crack nucleation life was reduced with increasing stress concentration, on the other hand the crack propagation life increased. The experimental fatigue results, originally expressed in terms of nominal shear stress amplitude, have been reanalysed by means of the local strain energy density (SED averaged over a control volume having radius R0 surrounding the notch tip. To exclude all extrinsic effects acting during the fatigue crack propagation phase, such as sliding contact and/or friction between fracture surfaces, crack initiation life has been considered in the present work. In the original paper, initiation life was defined in correspondence of a 0.1÷0.4-mm-deep crack. The control radius R0 for fatigue strength assessment of notched components, thought of as a material property, has been estimated by imposing the constancy of the averaged SED for both smooth and cracked specimens at NA = 2 million loading cycles
Prevention of shrinkage cracking in tight concrete structures
International Nuclear Information System (INIS)
Alvaredo, A.M.; Wittmann, F.H.
1995-01-01
It is shown that crack formation and propagation in concrete members subjected to restrained shrinkage can be realistically predicted by means of a comprehensive approach including a diffusion analysis and fracture mechanics considerations. The conditions for stable crack propagation regarding dimensions of the concrete member, degree of restraint to the imposed deformation and material properties are discussed. Guidelines on the prevention of shrinkage cracking of concrete structures are given. (author). 10 refs., 5 figs
Fatigue crack threshold relevant to stress ratio, crack wake and loading histories
International Nuclear Information System (INIS)
Okazaki, Masakazu; Iwasaki, Akira; Kasahara, Naoto
2013-01-01
Fatigue crack propagation behavior was investigated in a low alloy steel which experienced several kind of loading histories. Both the effects of stress ratio, test temperature on the fatigue crack threshold, and the change in the threshold depending on the thermo-mechanical loading histories, were experimentally investigated. It was shown that the thermo-mechanical loading history left its effect along the prior fatigue crack wake resulting in the change of fatigue crack threshold. Some discussions are made on how this type of loading history effect should be treated from engineering point of view. (author)
Experimental and Numerical Study of Interface Crack Propagation in Foam Cored Sandwich Beams
DEFF Research Database (Denmark)
Berggreen, Carl Christian; Simonsen, Bo Cerup; Borum, Kaj Kvisgård
2007-01-01
application example is to tear off one of the face laminates from the sandwich. This configuration can be found in many applications but is considered here to be occurring in a ship structure, particularly at the hard spot where the superstructure meets the deck. Face tearing experiments are carried out...... experiments and theory. For cores with higher density, the crack tends to propagate in the laminate itself with extensive fiber bridging leading to rather conservative numerical predictions. However, for structural configurations where LEFM can be applied, the presented procedure is sufficiently robust...... and accurate to be used in a number of important engineering applications, for example risk-based inspection and repair schemes....
Characteristics of SCC crack propagation in 22Cr-5. 5Ni-3Mo duplex stainless steel weldment
Energy Technology Data Exchange (ETDEWEB)
Kim, Choong Un; Kang, Choon Sik
1988-02-01
The characteristics of SCC crack propagation in duplex stainless steel weldment made by SMAW, GTAW and GMAW processes were investigated in 42% MgCl/sub 2/ 142 deg C boiling solution. From these experiments, it could be concluded that the structure anisotropy of ..gamma.. phase as well as the phase ratio played an important role in SCC resistance. GTA and GMA weld metal showed higher SCC resistance than base metal because of randomly distributed ..gamma.. phase. The crack in weld metal had same opportunity of receiving keying effect as that in base metal, but it had less possibility of intersecting ..gamma.. phase. The SCC resistance of the SMA weld metal and the HAZ was lower than that of the base metal because their phase ratio deviated from the proper phase ratio.
Energy Technology Data Exchange (ETDEWEB)
Helfer, Th
2006-03-15
This thesis aims to model the cracking of pressurised water reactor fuel pellets and its consequences on the mechanical behaviour of the fuel rod. Fuel cracking has two main consequences. It relieves the stress in the pellet, upon which the majority of the mechanical and physico-chemical phenomena are dependent. It also leads to pellet fragmentation. Taking fuel cracking into account is therefore necessary to adequately predict the mechanical loading of the cladding during the course of an irradiation. The local approach to fracture was chosen to describe fuel pellet cracking. Practical considerations brought us to favour a quasi-static description of fuel cracking by means of a local damage models. These models describe the appearance of cracks by a local loss of rigidity of the material. Such a description leads to numerical difficulties, such as mesh dependency of the results and abrupt changes in the equilibrium state of the mechanical structure during unstable crack propagations. A particular attention was paid to these difficulties because they condition the use of such models in engineering studies. This work was performed within the framework of the ALCYONE fuel performance package developed at CEA/DEC/SESC which relies on the PLEIADES software platform. ALCYONE provides users with various approaches for modelling nuclear fuel behaviour, which differ in terms of the type geometry considered for the fuel rod. A specific model was developed and implemented to describe fuel cracking for each of these approaches. The 2D axisymmetric fuel rod model is the most innovative and was particularly studied. We show that it is able to assess, thanks to an appropriate description of fuel cracking, the main geometrical changes of the fuel rod occurring under normal and off-normal operating conditions. (author)
Modelling the tearing crack growth in a ductile ferritic steel using X-FEM elements
International Nuclear Information System (INIS)
Simatos, A.; Prabel, B.; Marie, S.; Nedelec, M.; Combescure, A.
2012-01-01
Extended Finite Element Method (X-FEM) is used to model a cracked structure without meshing explicitly the crack. Indeed, the crack is represented by a discontinuity of the displacement field through additional degrees of freedom using Heaviside type function or derived from the Irwin's singular fields. Initially, the stress integration in the XFEM framework supposed to divide the cut elements into sub-triangles that are conform to the crack. This was motivated in order to integrate the behaviour accurately on both sides of the crack in particular at proximity of the crack tip where singular enrichments are present. This strategy induces field projections from the usual Gauss point configuration to a variable new one that depends on the crack position in the element. For ductile fracture modelization, this approach is not applicable, because in presence of large scale yield, the projection of internal variable fields is not conservative, in particular at proximity of the crack tip. In order to circumvent this problem, a new integration strategy was proposed by B. Prabel. It consists in using 64 Gauss points that are placed without regards to the crack position. This simple integration scheme permits to take implicitly into account the crack position and the fields in the element in an accurate and consistent way. This strategy was used in problem calculation for which the plastic radius remained small. It allowed introducing the over integrated elements in the probable propagation zone, just before plastification. In the case of ductile tearing, the plasticity is not confined near the crack tip and an improvement of the proposed strategy is made. This is then used to model large ductile crack growth in a ductile ferritic steel. To validate the predictions, the modelization is compared to a second F.E. calculation using the node release technique for the crack propagation. It is then shown that the two predictions are strictly equivalents. (authors)
Fracture dynamics of a propagating crack in a pressurized ductile cylinder
International Nuclear Information System (INIS)
Emery, A.F.; Love, W.J.; Kobayashi, A.S.
1977-01-01
A suddenly-introduced axial through-crack in the wall of a pipe pressurized by hot water is allowed to propagate according to Weiss' notch-strength theory of ductile static fracture. The dynamic-fracture criterion used enabled the authors to obtain a unique comparison of the results of ductile-fracture with those of brittle-fracture in a fracturing A533B steel pipe. Since the pipe cross-sectional area is likely to increase with large flap motions under ductile tearing, a large deformation shell-finite-difference-dynamic-code which includes rotary inertia was used in this analysis. The uniaxial-stress-strain curve of A533B steel was approximated by a bilinear-stress-strain where Von-Mises yield criterion and associated flow rule were used in the elastic-plastic analysis. The fluid pressure was assumed constant and thus pipe flaps are only lightly loaded by pressure in this analysis. (Auth.)
Stable propagation of interacting crack systems and modeling of damage
International Nuclear Information System (INIS)
Bazant, Z.P.; Tabbara, M.R.
1989-01-01
This paper presents general thermodynamic criteria for the stable states and stable path of structures with an interacting system of cracks. In combination with numerical finite element results for various cracked structure geometries, these criteria indicate that the crack response path of structures may exhibit bifurcations, after which the symmetry of the crack system is broken and some cracks grow preferentially. The problem is of interest for the prediction of ultimate loads, ductility and energy absorption capability of nuclear concrete structures as well as structures made of composites and ceramics
Effects of plastic anisotropy on crack-tip behaviour
DEFF Research Database (Denmark)
Legarth, Brian Nyvang; Tvergaard, Viggo; Kuroda, Mitsutoshi
2002-01-01
For a crack in a homogeneous material the effect of plastic anisotropy on crack-tip blunting and on the near-tip stress and strain fields is analyzed numerically. The full finite strain analyses are carried out for plane strain under small scale yielding conditions, with purely symmetric mode I...... loading remote from the crack-tip. In cases where the principal axes of the anisotropy are inclined to the plane of the crack it is found that the plastic zones as well as the stress and strain fields just around the blunted tip of the crack become non-symmetric. In these cases the peak strain...... on the blunted tip occurs off the center line of the crack, thus indicating that the crack may want to grow in a different direction. When the anisotropic axes are parallel to the crack symmetry is retained, but the plastic zones and the near-tip fields still differ from those predicted by standard isotropic...
On the controlling parameters for fatigue-crack threshold at low homologous temperatures
International Nuclear Information System (INIS)
Yu, W.; Gerberich, W.W.
1983-01-01
Fatigue crack propagation phenomena near the threshold stress intensity level ΔK /SUB TH/ , has been a vigorously studied topic in recent years. Near threshold the crack propagates rather slowly, thus giving enough time for various physical and chemical reactions to take place. Room air, which is the most commonly encountered environment, can still supply various ingredients such as oxygen, water vapor (and thus hydrogen) to support these reactions. Much effort had been directed toward the environmental aspects of near threshold fatigue crack growth. By conducting tests under vacuum, Suresh and coworkers found that the crack propagation rate in a 2-1/4 Cr-1Mo steel was higher in vacuum than in air. An oxide induced closure, which served to reduce the effective stress intensity at the crack tip, seems to furnish a good explanation. Neumann and coworkers proposed that during the fatigue process, extrusion-intrusion pairs can develop as a consequence of reversed slip around the crack tip when the crack was propagated near threshold stress intensity. Beevers demonstrated that fatigue fracture surfaces contact each other during unloading even under tension-tension cycling. Kanninen and Atkinson also reached the conclusion that the compressive stress acting at the crack tip due to residual plasticity can induce closure. Microstructural effects have also been cited as important factors in near threshold crack growth. It is generally accepted that coarser grains have a beneficial effect on the resistance to the near threshold crack propagation
Correlation Between Pin Misalignment and Crack Length in THT Solder Joints
Directory of Open Access Journals (Sweden)
Molnar A.
2017-06-01
Full Text Available In this manuscript, correlations were searched for between pin misalignments relative to PCB bores and crack propagation after cyclic thermal shock tests in THT solder joints produced from lead-free solder alloys. In total, 7 compositions were examined including SAC solders with varying Ag, Cu and Ni contents. The crack propagation was initiated by cyclic thermal shock tests with 40°C / +125°C temperature profiles. Pin misalignments relative to the bores were characterized with three attributes obtained from one section of the examined solder joints. Cracks typically originated at the solder/pin or solder/bore interfaces and propagated within the solder. It was shown that pin misalignments did not have an effect on crack propagation, thus, the solder joints’ lifetime.
International Nuclear Information System (INIS)
Arora, Punit; Tripathi, R.; Singh, P.K.; Bhasin, V.; Vijayan, P.K.
2016-01-01
The objective of the present study is to understand the Fatigue Crack Growth Rate (FCGR) behaviour after single over-load/ under-load event on carbon steel piping material. The tests have been carried out on standard Compact Tension (CT) specimens. The effect of different crack length to width ratio (a/W) of specimen and overload/under-load ratios on FCGR have been studied. The studies have shown significant reduction in FCG rate after overload event. The strain field has been measured using Digital Image Correlation (DIC) technique ahead of the crack tip to quantify the plastic zone size due to overload and constant amplitude load. In addition, plastic zone calculations have also been carried out using 3D finite element analyses for the prediction of post overload FCGR/ life. The predicted FCGR are in agreement with experimentally determined FCGR. (author)
Internal shear cracking in bulk metal forming
DEFF Research Database (Denmark)
Christiansen, Peter; Nielsen, Chris Valentin; Bay, Niels Oluf
2017-01-01
This paper presents an uncoupled ductile damage criterion for modelling the opening and propagation of internal shear cracks in bulk metal forming. The criterion is built upon the original work on the motion of a hole subjected to shear with superimposed tensile stress triaxiality and its overall...... performance is evaluated by means of side-pressing formability tests in Aluminium AA2007-T6 subjected to different levels of pre-strain. Results show that the new proposed criterionis able to combine simplicity with efficiency for predicting the onset of fracture and the crack propagation path for the entire...... cracking to internal cracks formed undert hree-dimensional states of stress that are typical of bulk metal forming....
The influence of microstructure on fatigue crack initiation in spheroidal graphite cast irons
International Nuclear Information System (INIS)
Starkey, M.S.; Irving, P.E.
1979-01-01
This paper reports the first stage of this work which concentrates on fatigue crack initiation with particular emphasis on the influence of microstructure. The fatigue lives of three fully ferritic and two fully pearlitic irons, each with different graphite nodule size distributions, have been determined at two strain amplitudes, 0.005 and 0.00018. The tests were carried out in fully reversed strain control on smooth cylindrical specimens in a servohydraulic testing machine. The effects of matrix structure and strength were clearly seen in that the pearlitic irons were superior at both strain levels. Nodule size on the other hand appeared to have no significant effect. The crack initiation sites in the specimens were located by interrupting the tests on detection of a 5% tensile load drop and heat tinting, before continuing. After failure, which was defined as complete separation, the fracture faces were examined on the scanning electron microscope. In the majority of the specimens the major crack origin was found to be a surface micropore with depths ranging from 50 to 250 μm. It is suggested that these micropores and not the graphite modules strongly influence the crack initiation behaviour in SG iron. These findings were confirmed by monitoring the initiation and growth of surface cracks from micropores using surface replica techniques. The influence of microstructure on the percentage of life spent in initiating and propagating a crack was thus determined. Hence the factors contributing to the fatigue behaviour of SG irons can be quantified. Their influence on predictions of cycles to crack initiation using the local approach is discussed. (orig.) 891 RW/orig. 892 RKD [de
Experimental and theoretical investigations on the behaviour of cracks in primary coolant piping
International Nuclear Information System (INIS)
Steinbuch, R.; Bartholome, G.; Felski, N.; Kastner, W.
1981-01-01
During the investigations of the government-sponsored R+D programs (RS 104 and RS 320) experimental and theoretical work has been performed to describe the leak before break behaviour and the extent of instable crack growth. The test pipes are 300 mm ID pipes made of 20MnMoNi55. Three of them had been welded to a pressure reservoir to simulate the situation of a real system of piping and components as related to hydrodynamics. The instrumentation of the specimen was designed to describe - temperature and pressure during failure - effect of reservoir on depressurisation - motion of the pipe - leakage area as function of time - crack arrest length. At two experiments the pressure dropped to saturation but in others for a short period the pressure was remarkably lower. (orig./GL)
Cracks propagation by stress corrosion cracking in conditions of Boiling Water Reactor (BWR)
International Nuclear Information System (INIS)
Fuentes C, P.
2003-01-01
This work presents the results of the assays carried out in the Laboratory of Hot Cells of the National Institute of Nuclear Research (ININ) to a type test tube Compact Tension (CT), built in steel austenitic stainless type 304L, simulating those conditions those that it operates a Boiling Water Reactor (BWR), at temperature 288 C and pressure of 8 MPa, to determine the speed to which the cracks spread in this material that is of the one that different components of a reactor are made, among those that it highlights the reactor core vessel. The application of the Hydrogen Chemistry of the Water is presented (HWC) that is one alternative to diminish the corrosion effect low stress in the component, this is gets controlling the quantity of oxygen and of hydrogen as well as the conductivity of the water. The rehearsal is made following the principles of the Mechanics of Elastic Lineal Fracture (LEFM) that considers a crack of defined size with little plastic deformation in the tip of this; the measurement of crack advance is continued with the technique of potential drop of direct current of alternating signal, this is contained inside the standard Astm E-647 (Method of Test Standard for the Measurement of Speed of Growth of Crack by fatigue) that is the one that indicates us as carrying out this test. The specifications that should complete the test tubes that are rehearsed as for their dimensions, it forms, finish and determination of mechanical properties (tenacity to the fracture mainly) they are contained inside the norm Astm E-399, the one which it is also based on the principles of the fracture mechanics. The obtained results were part of a database to be compared with those of other rehearsals under different conditions, Normal Chemistry of the Water (NWC) and it dilutes with high content of O 2 ; to determine the conditions that slow more the phenomena of stress corrosion cracking, as well as the effectiveness of the used chemistry and of the method of
International Nuclear Information System (INIS)
Gubeljak, N; Predan, J; Senčič, B; Chapetti, M D
2016-01-01
An integrated fracture mechanics approach is proposed to account for the estimation of the fatigue resistance of component. Applications, estimations and results showed very good agreements with experimental results. The model is simple to apply, accounts for the main geometrical, mechanical and material parameters that define the fatigue resistance, and allows accurate predictions. It offers a change in design philosophy: It could be used for design, while simultaneously dealing with crack propagation thresholds. Furthermore, it allows quantification of the material defect sensitivity. In the case of the set of fatigue tests carried out by rotational bending of specimens without residual stresses, the estimated results showed good agreement and that an initial crack length of 0.5 mm can conservatively explain experimental data. In the case of fatigue tests carried out on the springs at their final condition with bending at R = 0.1 our data shows the influence of compressive residual stresses on fatigue strength. Results also showed that the procedures allow us to analyze the different combinations of initial crack length and residual stress levels, and how much the fatigue resistance can change by changing that configuration. For this set of tests, the fatigue resistance estimated for an initial crack length equal to 0.35 mm, can explain all testing data observed for the springs. (paper)
Failure behaviour of a piping system with a circumferentially orientated flaw
International Nuclear Information System (INIS)
Mikkola, T.P.J.; Diem, H.; Blind, D.; Hunger, H.
1987-01-01
The experiments were conducted on the recently installed feedwater line of the HDR reactor in Kahl. The investigations were focused on analysing both the crack propagation of a circumferentially flowed pipe under the influence of corrosion and cyclic load, together with the pipeline's subsequent failure behaviour. The experimental conditions were selected in a manner representing those which can, for example, prevait during start-up or shut-down of reactor. To this aim, the pipes were internally stressed with high pressure and temperature oxygenic water in conjunction with an externally applied bending moment. The investigations are supplemented by elastic-plastic triaxial finite element (FE) calculations for various assumed crack configurations, both prior to and following the experiments, thus granting a fracture-mechanical assessment of the structural behaviour. (orig./DG) [de
Energy Technology Data Exchange (ETDEWEB)
Le Roux, J.Ch
2000-07-01
Cast duplex stainless steels are commonly used in components of pressurized water reactors primary circuit. When submitted to in-service temperatures embrittlement occurs because of the nucleation and growth of a harder phase in the ferrite by spinodal composition. Macrostructure of this steel (ferritic primary grain size is about 4-5 mm) and embrittlement of ferrite due to aging lead to a very high scattering of mechanical properties for monotonous loadings. We showed that, in spite of this macrostructure, the cyclic behaviour of aged duplex stainless steels fits usual Manson-Coffin law while initial hardening is followed by softening, in part because of the demodulation of the composition. The fatigue crack propagation rate of material follows a Paris law. While crack initiation mainly appears next to the millimetric cast defects, fatigue crack propagation remains a continuous mechanism. Ferritic and austenitic elements break successively (ferrite first breaks by cleavage, then austenite breaks by ductile fatigue). In spite of the fact that the aged ferrite is embrittled, cleavage microcracks, for load levels examined, seldom appear in ferrite at the crack tip and on both sides of the main crack. Effects of cast defects and crystallographic ferrite orientation were also studied. Propagation fatigue crack behaviour was modeled assuming that the crack tip material behaves as if it was submitted to low cycle fatigue loadings. If we consider a homogeneous material, results are in good agreement with experiments. (authors)
lnvestigation of Patch Coatings lnfluence on the Stress lntensity Factor for Surface Cracks
DEFF Research Database (Denmark)
Lambertsen, Søren Heide; Jepsen, Michael S.; Damkilde, Lars
2013-01-01
In this paper, it is investigated how a surface layer of epoxy glue will affect the crack propagation of a surface crack. The intension is to reduce or even stop the crack propagation by means of patch layer coating. When adding a patch layer to the surface with small cracks, the layer will attem...
International Nuclear Information System (INIS)
Babaev, A.V.; Knysh, V.V.; Labunskaya, N.F.
1985-01-01
Dependences permitting to determine by calculation method the duration of the stage of fatigue crack propagation in joints with poor penetration and residual stresses are obtained on the basis of criteria of fracture mechanics. It gives a possibility to estimate the resource of these joints using the calculation-experimental method
Modelling probabilistic fatigue crack propagation rates for a mild structural steel
Correia, J.A.F.O.; de Jesus, A.M.P.; Fernández-Canteli, A.
2014-01-01
A class of fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and local strain-life damage models have been proposed in literature. The fatigue crack growth is regarded as a process of continuous crack initializations over successive elementary material blocks, which may be governed by smooth strain-life damage data. Some approaches account for the residual stresses developing at the crack tip in the actual crack driving force asse...
Directory of Open Access Journals (Sweden)
Othman Al-Khudairi
2017-10-01
Full Text Available In this paper, the sensitivity of the structural integrity of wind turbine blades to debonding of the shear web from the spar cap was investigated. In this regard, modal analysis, static and fatigue testing were performed on a 45.7 m blade for three states of the blade: (i as received blade (ii when a crack of 200 mm was introduced between the web and the spar cap and (iii when the crack was extended to 1000 mm. Calibration pull-tests for all three states of the blade were performed to obtain the strain-bending moment relationship of the blade according to the estimated target bending moment (BM which the blade is expected to experience in its service life. The resultant data was used to apply appropriate load in the fatigue tests. The blade natural frequencies in flapwise and edgewise directions over a range of frequency domain were found by modal testing for all three states of the blade. The blade first natural frequency for each state was used for the flapwise fatigue tests. These were performed in accordance with technical specification IEC TS 61400-23. The fatigue results showed that, for a 200 mm crack between the web and spar cap at 9 m from the blade root, the crack did not propagate at 50% of the target BM up to 62,110 cycles. However, when the load was increased to 70% of target BM, some damages were detected on the pressure side of the blade. When the 200 mm crack was extended to 1000 mm, the crack began to propagate when the applied load exceeded 100% of target BM and the blade experienced delaminations, adhesive joint failure, compression failure and sandwich core failure.
Al-Khudairi, Othman; Hadavinia, Homayoun; Little, Christian; Gillmore, Gavin; Greaves, Peter; Dyer, Kirsten
2017-10-03
In this paper, the sensitivity of the structural integrity of wind turbine blades to debonding of the shear web from the spar cap was investigated. In this regard, modal analysis, static and fatigue testing were performed on a 45.7 m blade for three states of the blade: (i) as received blade (ii) when a crack of 200 mm was introduced between the web and the spar cap and (iii) when the crack was extended to 1000 mm. Calibration pull-tests for all three states of the blade were performed to obtain the strain-bending moment relationship of the blade according to the estimated target bending moment (BM) which the blade is expected to experience in its service life. The resultant data was used to apply appropriate load in the fatigue tests. The blade natural frequencies in flapwise and edgewise directions over a range of frequency domain were found by modal testing for all three states of the blade. The blade first natural frequency for each state was used for the flapwise fatigue tests. These were performed in accordance with technical specification IEC TS 61400-23. The fatigue results showed that, for a 200 mm crack between the web and spar cap at 9 m from the blade root, the crack did not propagate at 50% of the target BM up to 62,110 cycles. However, when the load was increased to 70% of target BM, some damages were detected on the pressure side of the blade. When the 200 mm crack was extended to 1000 mm, the crack began to propagate when the applied load exceeded 100% of target BM and the blade experienced delaminations, adhesive joint failure, compression failure and sandwich core failure.
Fatigue crack retardation of high strength steel in saltwater
International Nuclear Information System (INIS)
Tokaji, K.; Ando, Z.; Imai, T.; Kojima, T.
1983-01-01
A high strength steel was studied in 3 percent saltwater to investigate the effects of a corrosive environment and sheer thickness on fatigue crack propagation behavior following the application of a single tensile overload. Experiments were carried out under sinusoidally varying loads at a load ratio of 0 and frequency of 10 H /SUB z/ . A single tensile overload was found to cause delayed retardation, and the crack propagation rate at first increased, followed by fairly rapid decrease to a minimum value and then increased gradually to its steady-state value, just as it did in air. The overload affected zone size and the retardation cycles increased with decreasing sheet thickness, just as they did in air. However, the zone size and the cycles were larger in 3 percent saltwater than in air. Since the crack propagation rates through the overload affected zone were not affected by the test environment, the longer retardation cycles in 3 percent saltwater were attributed to an enlargement of the overload affected zone size. The crack propagation behavior following the application of a single tensile overload in 3 percent saltwater was well explained by the crack closure concept
The vibrational behaviour of a cracked turbine rotor
International Nuclear Information System (INIS)
Grabowski, B.
1978-01-01
In order to detect an incipient crack on a turbine rotor with the aid of measurement of the shaft vibrations, these must be known in the first place the effects of a crack on the vibrational behavior of a rotor. For this purpose a method using the modal analysis is presented here. The rigidity depending on the angle of rotation at the position of the crack is accounted for by means of a model. Because of the composition of the computer code there may also be worked with measured values for the rigidity. The results of the calculations show that within the range of speeds, in which for many turbines the operating speed lies, a crack will cause distinct variations of the shaft vibrations. The crack stimulates vibrations with frequencies of rotation and frequencies of double-rotation. Both may be used for crack detection. Because of the strong dependence of the size of the amplitudes of vibration on the design of the rotor and the position of the crack each rotor should be subject to a detailed crack calculation for a better judgement of the measured values. (orig.) [de
International Nuclear Information System (INIS)
Liu, X; Luo, Y Y; Wang, Z W
2014-01-01
As an important component of the blade-control system in Kaplan turbines, piston rods are subjected to fluctuating forces transferred by the turbines blades from hydraulic pressure oscillations. Damage due to unsteady hydraulic loads might generate unexpected down time and high repair cost. In one running hydropower plant, the fracture failure of the piston rod was found twice at the same location. With the transient dynamic analysis, the retainer ring structure of the piston rod existed a relative high stress concentration. This predicted position of the stress concentration agreed well with the actual fracture position in the plant. However, the local strain approach was not able to explain why this position broke frequently. Since traditional structural fatigue analyses use a local stress strain approach to assess structural integrity, do not consider the effect of flaws which can significantly degrade structural life. Using linear elastic fracture mechanism (LEFM) approaches that include the effect of flaws is becoming common practice in many industries. In this research, a case involving a small semi-ellipse crack was taken into account at the stress concentration area, crack growth progress was calculated by FEM. The relationship between crack length and remaining life was obtained. The crack propagation path approximately agreed with the actual fracture section. The results showed that presence of the crack had significantly changed the local stress and strain distributions of the piston rod compared with non-flaw assumption
Liu, X.; Y Luo, Y.; Wang, Z. W.
2014-03-01
As an important component of the blade-control system in Kaplan turbines, piston rods are subjected to fluctuating forces transferred by the turbines blades from hydraulic pressure oscillations. Damage due to unsteady hydraulic loads might generate unexpected down time and high repair cost. In one running hydropower plant, the fracture failure of the piston rod was found twice at the same location. With the transient dynamic analysis, the retainer ring structure of the piston rod existed a relative high stress concentration. This predicted position of the stress concentration agreed well with the actual fracture position in the plant. However, the local strain approach was not able to explain why this position broke frequently. Since traditional structural fatigue analyses use a local stress strain approach to assess structural integrity, do not consider the effect of flaws which can significantly degrade structural life. Using linear elastic fracture mechanism (LEFM) approaches that include the effect of flaws is becoming common practice in many industries. In this research, a case involving a small semi-ellipse crack was taken into account at the stress concentration area, crack growth progress was calculated by FEM. The relationship between crack length and remaining life was obtained. The crack propagation path approximately agreed with the actual fracture section. The results showed that presence of the crack had significantly changed the local stress and strain distributions of the piston rod compared with non-flaw assumption.
International Nuclear Information System (INIS)
Tice, D.R.; Stairmand, J.W.; Fairbrother, H.J.; Stock, A.
2007-01-01
Although austenitic stainless steels do not show a high degree of susceptibility to stress corrosion cracking (SCC) in PWR primary environments, there is limited evidence from laboratory testing that crack propagation may occur under some conditions for materials in a cold-worked condition. A test program is therefore underway to examine the factors influencing SCC propagation in good quality PWR primary coolant. Type 304 stainless steel was subjected to cold working by either rolling (at ambient or elevated temperature) or fatigue cycling, to produce a range of yield strengths. Compact tension specimens were fabricated from these materials and tested in simulated high temperature (250-300 o C) PWR primary coolant. It was observed that the degree of crack propagation was influenced by the degree of cold work, the crack growth orientation relative to the rolling direction and the method of working. (author)
Energy Technology Data Exchange (ETDEWEB)
Gong, Xing, E-mail: gongxingzfl@hotmail.com [SCK-CEN (Belgian Nuclear Research Centre), Boeretang 200, B-2400 Mol (Belgium); KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Marmy, Pierre, E-mail: pierre.marmy@sckcen.be [SCK-CEN (Belgian Nuclear Research Centre), Boeretang 200, B-2400 Mol (Belgium); Qin, Ling, E-mail: Ling.Qin@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Verlinden, Bert, E-mail: Bert.Verlinden@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Wevers, Martine, E-mail: Martine.Wevers@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Seefeldt, Marc, E-mail: Marc.Seefeldt@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium)
2014-11-17
The low cycle fatigue properties of a modified 9Cr–1Mo ferritic–martensitic steel (T91) have been tested in stagnant liquid lead–bismuth eutectic (LBE) with oxygen concentrations ranging from 1.16×10{sup −6} to 6.0×10{sup −10} wt% at 350 °C. The effect of liquid metal embrittlement (LME) on fatigue endurance, fatigue crack propagation modes and secondary cracking has been studied. The results showed that the fatigue lives of T91 steel in a low oxygen concentration LBE were drastically reduced compared to those in vacuum due to the presence of LME. The microstructural observations on the fatigue crack propagation modes revealed that fatigue cracks in LBE mainly propagate across prior-austenite grain boundaries and then cut through martensitic lath boundaries, simultaneously leaving a few plastic flow traces and characteristic brittle features. Intergranular and interlath cracking occurred occasionally and their occurrence depended on the orientation of the boundaries relative to the stress axis. The complexity of the LME-induced fracture features can be attributed to a mixture of the multiple failure modes. No obvious plastic shear strain localization was present around the crack tips when LME occurred. However, using a high resolution electron backscatter diffraction (EBSD) technique, highly localized plastic shear strain was observed in the vicinity of the crack tips in vacuum, manifested by the presence of very fine subgrains along the crack walls. A qualitative mechanism was proposed to account for the LME phenomenon in the T91/LBE system. In addition, the secondary cracking at fatigue striations was different in the presence of LBE compared to vacuum. This phenomenon was elucidated by taking into account the influence of the LME on the fatigue crack propagation rate.
Fatigue Crack Propagation Simulation in Plane Stress Constraint
DEFF Research Database (Denmark)
Ricardo, Luiz Carlos Hernandes; Spinelli, Dirceu
2010-01-01
Nowadays, structural and materials engineers develop structures and materials properties using finite element method. This work presents a numerical determination of fatigue crack opening and closure stress intensity factors of a C(T) specimen. Two different standard variable spectrum loadings...... are utilized, Mini-Falstaff and Wisper. The effects in two-dimensional (2D) small scale yielding models of fatigue crack growth were studied considering plane stress constraint....
On the thermally activated crack propagation in alumina
International Nuclear Information System (INIS)
Devezas, T.C.
1983-01-01
Subcritical crack growth was studied in the temperature 25-100 0 C in two commercial aluminas containing different amounts of a glassy phase. The experimental method employed was that of double torsion under constant load, using a device specially built to carry out mechanical tests at constant compressive load and high temperatures. Activation enthalpies of subcritical crack growth were determined for the two materials. (Author) [pt
International Nuclear Information System (INIS)
Oikonomidis, F.; Shterenlikht, A.; Truman, C.E.
2014-01-01
Part 1 of this paper described a specimen for the measurement of high strain rate flow and fracture properties of pipe material and for tuning a strain rate dependent damage model (SRDD). In part 2 the tuned SRDD model is used for the simulation of axial crack propagation and arrest in X100 natural gas pipelines. Linear pressure drop model was adopted behind the crack tip, and an exponential gas depressurisation model was used ahead of the crack tip. The model correctly predicted the crack initiation (burst) pressure, the crack speed and the crack arrest length. Strain rates between 1000 s −1 and 3000 s −1 immediately ahead of the crack tip are predicted, giving a strong indication that a strain rate material model is required for the structural integrity assessment of the natural gas pipelines. The models predict the stress triaxiality of about 0.65 for at least 1 m ahead of the crack tip, gradually dropping to 0.5 at distances of about 5–7 m ahead of the crack tip. Finally, the models predicted a linear drop in crack tip opening angle (CTOA) from about 11−12° at the onset of crack propagation down to 7−8° at crack arrest. Only the lower of these values agree with those reported in the literature for quasi-static measurements. This discrepancy might indicate substantial strain rate dependence in CTOA. - Highlights: • Finite element simulations of 3 burst tests of X100 pipes are detailed. • Strain rate dependent damage model, tuned on small scale X100 samples, was used. • The models correctly predict burst pressure, crack speed and crack arrest length. • The model predicts a crack length dependent critical CTOA. • The strain rate dependent damage model is verified as mesh independent
DEFF Research Database (Denmark)
Martakos, G.; Andreasen, J.H.; Berggreen, Christian
2017-01-01
A recently proposed face-sheet–core interface crack arresting device is implemented in sandwich beams and tested using the Sandwich Tear Test configuration. Fatigue loading conditions are applied to propagate the crack and determine the effect of the crack stopper on the fatigue growth rate and a...
DEFF Research Database (Denmark)
Nielsen, Lars Vendelbo
An effort has been undertaken in order to develop a concept for evaluation of the risk of hydrogen-assisted cracking in cathodically protected gas transmission pipelines. The effort was divided into the following subtasks: A. Establish a correlation between the fracture mechanical properties...... crack propagation. This resulted in threshold curves that can be used for assessment of the risk of hydrogen-assisted cracking as a function of operating pressure and hydrogen content - having the flaw size as discrete parameter. The results are to be used mainly on a conceptual basis......, but it was indicated that the requirements for crack propagation include an overprotective CP-condition, a severe sulphate-reducing environment, as well as a large flaw (8 mm or a leak in the present case). A 1 mm flaw (which may be the maximum realistic flaw size) is believed to be unable to provoke crack propagation...
Hydrogen Embrittlement Mechanism in Fatigue Behaviour of Austenitic and Martensitic Stainless Steels
Directory of Open Access Journals (Sweden)
Brück Sven
2018-01-01
Full Text Available In the present study, the influence of hydrogen on the fatigue behaviour of the high strength martensitic stainless steel X3CrNiMo13-4 and the metastable austenitic stainless steels X2Crni19-11 with various nickel contents was examined in the low and high cycle fatigue regime. The focus of the investigations was the changes in the mechanisms of short crack propagation. The aim of the ongoing investigation is to determine and quantitatively describe the predominant processes of hydrogen embrittlement and their influence on the short fatigue crack morphology and crack growth rate. In addition, simulations were carried out on the short fatigue crack growth, in order to develop a detailed insight into the hydrogen embrittlement mechanisms relevant for cyclic loading conditions.
Temperature effect on Zircaloy-4 stress corrosion cracking
International Nuclear Information System (INIS)
Farina, Silvia B.; Duffo, Gustavo S.; Galvele, Jose R.
1999-01-01
Stress corrosion cracking (SCC) susceptibility of Zircaloy-4 alloy in chloride, bromide and iodide solutions with variables as applied electrode potential, deformation rate and temperature have been studied. In those three halide solutions the susceptibility to SCC is only observed at potentials close to pitting potential, the crack propagation rate increases with the increase of deformation rate, and that the temperature has a notable effect only for iodide solutions. For chloride and bromide solutions and temperatures ranging between 20 to 90 C degrees it was not found measurable changes in crack propagation rates. (author)
Crack fronts and damage in glass at the nanometre scale
International Nuclear Information System (INIS)
Marliere, Christian; Prades, Silke; Celarie, Fabrice; Dalmas, Davy; Bonamy, Daniel; Guillot, Claude; Bouchaud, Elisabeth
2003-01-01
We have studied the low-speed fracture regime for different glassy materials with variable but controlled length scales of heterogeneity in a carefully controlled surrounding atmosphere. By using optical and atomic force microscopy techniques, we tracked, in real-time, the crack tip propagation at the nanometre scale over a wide velocity range (10 -3 -10 -12 m s -1 and below). The influence of the heterogeneities on this velocity is presented and discussed. Our experiments reveal also - for the first time - that the crack progresses through nucleation, growth and coalescence of nanometric damage cavities within the amorphous phase. This may explain the large fluctuations observed in the crack tip velocities for the smallest values. This behaviour is very similar to that involved, at the micrometric scale, in ductile fracture. The only difference is very probably due to the related length scales (nanometric instead of micrometric). The consequences of such a nano-ductile fracture mode observed at a temperature far below the glass transition temperature, T g , in glass is also discussed
Mechanical properties and flexure behaviour of lightweight foamed concrete incorporating coir fibre
Mohamad, Noridah; Afif Iman, Muhamad; Othuman Mydin, M. A.; Samad, A. A. A.; Rosli, J. A.; Noorwirdawati, A.
2018-04-01
This paper presents an experimental investigation on the mechanical properties and flexural behaviour of lightweight foamed concrete (LFC) with added coir fibre as filler. The compressive strength (Pt), tensile strength (Ft), modulus of elasticity (E), ultimate load and crack pattern of the foamed concrete were determined. The coir fibre was added to the foamed concrete mixture at 0.1%, 0.2% and 0.3% of the total weight of cement. Effects of various percentage of coir fibre used on foam concrete’s mechanical and properties and flexural behaviour were studied and analysed. It was found that the increase percentage of fibre resulted in increase in compressive strength, tensile strength and modulus of elasticity of LFC mixture. LFC with added coir of 0.3% experienced the smallest crack propagation.
International Nuclear Information System (INIS)
James, L.A.
1985-08-01
Section XI of the ASME Boiler and Pressure Vessel Code provides rules for the analysis of structures for which cracks or crack-like flaws have been discovered during inservice inspection. The Code provides rules for the analysis of both surface flaws as well as flaws that are embedded within the wall of the pressure vessel. In the case of surface flaws, the Code provides fatigue crack growth rate relationships for typical nuclear pressure vessel steels (e.g., ASTM A508-2 and A533-B) cycled in water environments typical of those in light-water reactors (LWR). However, for the case of embedded cracks, the Code provides crack growth relationships based on results from specimens that were cycled in an elevated temperature air environment. Although these latter relationships are often referred to as applying to ''inert'' environments, the results of this paper will show that an elevated temperature air environment is anything but inert, and that use of such relationships can result in overly pessimistic estimates of fatigue-crack growth lifetimes of embedded cracks. The reason, of course, is that embedded cracks grow in an environment that is probably much closer to a vacuum than an air environment
Czech Academy of Sciences Publication Activity Database
Kafka, Vratislav
2011-01-01
Roč. 56, č. 4 (2011), s. 343-358 ISSN 0001-7043 R&D Projects: GA ČR(CZ) GA103/09/2101 Institutional research plan: CEZ:AV0Z20710524 Keywords : crack propagation * nonlocal effect * deviatoric local effect * isotropic nonlocal Subject RIV: BM - Solid Matter Physics ; Magnetism
Crack growth rates in vessel head penetration materials
International Nuclear Information System (INIS)
Gomez Briceno, D.; Lapena, J.; Blazquez, F.
1994-01-01
The cracks detected in reactor vessel head penetrations in certain European plants have been attributed to Primary Water Stress Corrosion Cracking (PWSCC). The penetrations in question are made from Inconel 600. The susceptibility of this alloy to PWSCC has been widely studied in relation to use of this material for steam generator tubes. When the first reactor vessel head penetration cracks were detected, most of the available data on crack propagation rates were from test specimens made from steam generator tubes and tested under conditions that questioned the validity of these data for assessment of the evolution of cracks in penetrations. For this reason, the scope of the Spanish Research Project on the Inspection and Repair of PWR reactor vessel head penetrations included the acquisition of data on crack propagation rates in Inconel 600, representative of the materials used for vessel head penetrations. (authors). 1 fig., 2 tabs., 6 refs
Post-cracking Behaviour and Fracture Energy of Synthetic Fibre Reinforced Concrete
Directory of Open Access Journals (Sweden)
Marta KOSIOR-KAZBERUK
2016-11-01
Full Text Available The paper reports the results of experimental programme focused on the effect of various synthetic fibres on fracture properties and ductility of concrete. The fracture energy was assessed on beams with initial notches in three-point bend test. The incorporation of synthetic fibres had a slight effect on mechanical properties of concrete but, at the same time, it had a significant influence on the fracture energy by modification of post-cracking behaviour of concrete. It was found that the modern synthetic fibres might be able to impart significant toughness and ductility to concrete. However, the beneficial effect of fibres depends on their length and flexibility. The analysis of load-deflection curves obtained made it possible to fit the simple function, describing the post-peak behaviour of fibre reinforced concrete, which can be useful for the calculation of GF value.DOI: http://dx.doi.org/10.5755/j01.ms.22.4.13246
OBSERVATION OF FATIGUE CRACK PATHS IN NODULAR CAST IRON AND ADI MICROSTRUCTURES
Directory of Open Access Journals (Sweden)
Lukáš Bubenko
2009-07-01
Full Text Available When speaking about quality of construction materials, fatigue crack propagation resistance is one of the most important considered properties. That is essentially influenced by character of matrix. Here presented contribution deals with the fatigue crack propagation mode through the matrix of as-cast nodular cast iron (NCI and austempered ductile iron (ADI, whereas influence of microstructure has been considered and discussed. Experimental materials used in presented contribution were pearlitc-ferritic NCI and heat treated ADI 800. Pearlitic-ferritic NCI was used as the base for ADI production. Experiments were performed on mini round compact tension (RCT specimens using an Amsler vibrophore. Fatigue crack paths in both materials were investigated and compared. Light microscopy was used to analyze the microstructure, crack initiation and propagation within broken specimens. In both tested materials fatigue cracks always initiated at graphite-matrix interface, while graphite nodules remained generally unbroken, eventually only surface of nodules was damaged. Though, comparing two materials with different microstructures, the diversity of fatigue crack propagation modes at high deltaK and low deltaK was observed.
3D characterization of crack propagation in building stones
Fusi, N.; Martinez-Martinez, J.; Crosta, G. B.
2012-04-01
Opening of fractures can strongly modify mechanical characteristics of natural stones and thus significantly decrease stability of historical and modern buildings. It is commonly thought that fractures origin from pre-existing structures of the rocks, such as pores, veins, stylolythes (Meng and Pan, 2007; Yang et al., 2008). The aim of this study is to define relationships between crack formation and textural characteristics in massive carbonate lithologies and to follow the evolution of fractures with loading. Four well known Spanish building limestones and dolostones have been analysed: Amarillo Triana (AT): a yellow dolomitic marble, with fissures filled up by calcite and Fe oxides or hydroxides; Blanco Tranco (BT): a homogeneous white calcitic marble with pore clusters orientated parallel to metamorphic foliation; Crema Valencia (CV): a pinkish limestone (mudstone), characterized by abundant stilolythes, filled mainly by quartz (80%) and kaolin (11%); Rojo Cehegin (RC): a red fossiliferous limestone (packstone) with white veins, made up exclusively by calcite in crystals up to 300 micron. All lithotypes are characterized by homogeneous mineralogical composition (calcitic or dolomitic) and low porosity (<10%). Three cores 20 mm in diameter have been obtained for each lithotype. Uniaxial compressive tests have been carried out in order to induce sample fracturing by a series of successive steps with application of a progressive normal stress. Crack propagation has been checked after each stress level application by microCT-RX following Hg impregnation of the sample (in a Hg porosimeter). Combination of both tests (microCT-RX and Hg porosimeter) guarantees a better characterization of small defects and their progressive propagation inside low-porous rocks than by employing solely microCT-RX (Fusi et al., 2009). Due to the reduced dimensions of sample holder (dilatometers) in porosimeter, cores have been cut with a non standard h/d = 1.5. Several cycles of: a) Hg
International Nuclear Information System (INIS)
Aurich, D.; Gerwien, P.; Huenecke, J.; Klingbeil, D.; Krafka, H.; Kuenecke, G.; Ohm, K.; Veith, H.; Wossidlo, P.; Haecker, R.
1998-01-01
The crack growth resistance behaviour of the steels StE 460 and 22NiMoCr3-7 was determined in the temperature range from 23 C to 350 C by means of C(T), M(T), and ISO-V specimens tested under quasistatic and dynamic loads. The Russian steel 15Ch2NMFA-A was tested at room temperature and 50 C. In the steels StE 460 and 22 NiMoCr3-7, the minimum crack growth resistance is observed at about 250 C, with measured values always being higher for the latter steel type. The crack growth resistance behaviour of the tested materials correlates with the behaviour of flow curve, yield strength, and notch impact toughness as a function of temperature. Impact tests of ISO-V specimens give higher crack resistance values than quasistatic load tests, and the temperature dependence is significantly lower than those of specimens tested under static loads. A metallurgical analysis of the materials shows the causes of the dissimilar behaviour. The stretching zones determined for the C(T) specimen correspond to the toughness of the steels examined, and they are not much influenced by the temperature. The numerical analysis using damaging models for simulation of ductile crack growth is reported for all specimen types and two different temperatures each. (orig./CB) [de
Stress Corrosion Cracking of Zircaloy-4 in Halide Solutions: Effect of Temperature
Directory of Open Access Journals (Sweden)
Farina S.B.
2002-01-01
Full Text Available Zircaloy-4 was found to be susceptible to stress corrosion cracking in 1 M NaCl, 1 M KBr and 1 M KI aqueous solutions at potentials above the pitting potential. In all the solutions tested crack propagation was initially intergranular and then changed to transgranular. The effect of strain rate and temperature on the SCC propagation was investigated. An increase in the strain rate was found to lead to an increase in the crack propagation rate. The crack propagation rate increases in the three solutions tested as the temperatures increases between 20 and 90 °C. The Surface-Mobility SCC mechanism accounts for the observation made in the present work, and the activation energy predicted in iodide solutions is similar to that found in the literature.
Dislocations, the elastic energy momentum tensor and crack propagation
International Nuclear Information System (INIS)
Lung, Chi-wei
1979-07-01
Based upon dislocation theory, some stress intensity factors can be calculated for practical cases. The results obtained by this method have been found to agree fairly well with the results obtained by the conventional fracture mechanics. The elastic energy momentum tensor has been used to calculate the force acting on the crack tip. A discussion on the kinetics of migration of impurities to the crack tip was given. It seems that the crack tip sometimes may be considered as a singularity in an elastic field and the fundamental law of classical field theory is applicable on the problem in fracture of materials. (author)
Determination of I-SCC crack propagation rate of zircaloy-4
International Nuclear Information System (INIS)
Woo-Seog, Ryu
2002-01-01
Threshold stress intensity (K ISCC ) and propagation rate of iodine-induced SCC in recrystallized and stress-relieved Zircaloy-4 were determined using a DCPD method. Dynamic system flowing Ar gas through iodine chamber at 60 deg C provided a constant iodine pressure of 1000 Pa during test. The SCC curves of crack velocity vs. stress intensity showed the typical SCC curves that are composed of stages I, II and III. The threshold K ISCC at 350 deg C was about 9 and 9.5 MPa √m for the stress- relieved Zircaloy-4 and the recrystallized Zircaloy-4, respectively. The plateau velocity in the stage II at 350 deg C was 4-8x 10 -4 mm/sec in the range of 20-40 MPa√m. In comparison with recrystallized Zircaloy-4, stress-relieved Zircaloy-4 had a lower threshold stress intensity factor and a little higher SCC velocity, indicating that SRA Zircaloy-4 was more sensitive to SCC in respect of velocity. The fracture mode in recrystallized Zircaloy was mostly a transgranular fracture with river pattern. An intergranular mode and the flutting were scarcely observed. (author)
Analytical Model for Fictitious Crack Propagation in Concrete Beams
DEFF Research Database (Denmark)
Ulfkjær, J. P.; Krenk, Steen; Brincker, Rune
1995-01-01
An analytical model for load-displacement curves of concrete beams is presented. The load-displacement curve is obtained by combining two simple models. The fracture is modeled by a fictitious crack in an elastic layer around the midsection of the beam. Outside the elastic layer the deformations...... are modeled by beam theory. The state of stress in the elastic layer is assumed to depend bilinearly on local elongation corresponding to a linear softening relation for the fictitious crack. Results from the analytical model are compared with results from a more detailed model based on numerical methods...... for different beam sizes. The analytical model is shown to be in agreement with the numerical results if the thickness of the elastic layer is taken as half the beam depth. It is shown that the point on the load-displacement curve where the fictitious crack starts to develop and the point where the real crack...
Investigation of fretting behaviour in pressure armour layers of flexible pipes
Don Rasika Perera, Solangarachchige
The incidence of fretting damage in the pressure armour wires of flexible pipes used in offshore oil explorations has been investigated. A novel experimental facility which is capable of simulating nub and valley contact conditions of interlocking wire winding with dynamic slip, representative of actual pipe loading, has been developed. The test set-up is equipped with a state of the art data acquisition system and a controller with transducers to measure and control the normal load, slip amplitude and friction force at the contact, in addition to the hoop st